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((Short description|Decreased ability to see color or color differences))
((cs1 config|name-list-style=vanc))
((redirect|Colorblind|the disorder that causes most forms of color blindness|Congenital red–green color blindness|other uses|Color blind (disambiguation)))
((Use American English|date=March 2021))
((Use dmy dates|date=March 2021))
((Infobox medical condition (new)
| name          = Color blindness
| synonyms      = Color vision deficiency, impaired color vision<ref name=Gor1998/>
| image         = Ishihara 9.svg
| field         = [[Ophthalmology]]
| symptoms      = Decreased ability to [[color vision|see color]]s<ref name=NEI2015/>
| complications = 
| onset         = 
| duration      = Long term<ref name=NEI2015/>
| causes        = [[Genetics|Genetic]] ([[heredity|inherited]] usually [[X-linked]])<ref name=NEI2015/>
| risks         = 
| diagnosis     = [[Ishihara color test]]<ref name=NEI2015/>
| differential  = 
| prevention    = 
| treatment     = Adjustments to teaching methods, [[mobile apps]]<ref name=Gor1998/><ref name=NEI2015/>
| medication    = 
| prognosis     = 
| frequency     = Red–green: 8% males, 0.5% females (Northern European descent)<ref name=NEI2015/>
| deaths        = 
| caption       = Example of an [[Ishihara color test]] plate. Viewers with normal color vision should clearly see the number "74".
))

<!-- Description, Cause and Epidemiology -->
'''Color blindness''' or '''color vision deficiency''' ('''CVD''') is the decreased ability to [[color vision|see color]] or differences in [[color]].<ref name=NEI2015/> The severity of color blindness ranges from mostly unnoticeable to full absence of color perception. Color blindness is usually an [[Heredity|inherited]] problem or variation in the functionality of one or more of the three classes of [[cone cell]]s in the retina, which mediate color vision.<ref name=NEI2015/> The most common form is caused by a genetic condition called [[congenital red–green color blindness]] (including protan and deutan types), which affects ''up to'' 1 in 12 males (8%) and 1 in 200 females (0.5%).<ref name=NEI2015/><ref name="NHS">((Cite web |date=2017-10-18 |title=Colour vision deficiency (colour blindness) |url=https://www.nhs.uk/conditions/colour-vision-deficiency/ |access-date=2022-03-17 |website=nhs.uk |language=en))</ref> The condition is more prevalent in males, because the [[opsin]] genes responsible are located on the [[X chromosome]].<ref name=NEI2015/> Rarer genetic conditions causing color blindness include congenital blue–yellow color blindness (tritan type), [[blue cone monochromacy]], and [[achromatopsia]]. Color blindness can also result from physical or chemical damage to the [[eye]], the [[optic nerve]], parts of the [[brain]], or from medication toxicity.<ref name=NEI2015/> Color vision also naturally degrades in old age.<ref name=NEI2015/>

<!-- Diagnosis & Treatment -->
Diagnosis of color blindness is usually done with a [[color vision test]], such as the [[Ishihara test]]. There is no cure for most causes of color blindness, however there is ongoing research into [[Gene therapy for color blindness|gene therapy]] for some severe conditions causing color blindness.<ref name=NEI2015/> Minor forms of color blindness do not significantly affect daily life and the color blind automatically develop adaptations and coping mechanisms to compensate for the deficiency.<ref name=NEI2015/> However, diagnosis may allow an individual, or their parents/teachers to actively accommodate the condition.<ref name=Gor1998>((cite journal | vauthors = Gordon N | title = Colour blindness | journal = Public Health | volume = 112 | issue = 2 | pages = 81–4 | date = March 1998 | pmid = 9581449 | doi = 10.1038/sj.ph.1900446 ))</ref> [[Color blind glasses]] (e.g. ''[[EnChroma]]'') may help the red–green color blind at some [[color task]]s,<ref name=NEI2015/> but they do not grant the wearer "normal color vision" or the ability to see "new" colors.<ref name=Robledo>((cite journal |last1=Gómez-Robledo |first1=L |title=Do EnChroma glasses improve color vision for colorblind subjects? |journal=Optics Express |date=2018 |volume=26 |issue=22 |pages=28693–28703 |doi=10.1364/OE.26.028693|pmid=30470042 |bibcode=2018OExpr..2628693G |s2cid=53721875 |doi-access=free |hdl=10481/57698 |hdl-access=free ))</ref> Some [[mobile app]]s can use a device's camera to identify colors.<ref name=NEI2015>((cite web|title=Facts About Color Blindness|url=https://nei.nih.gov/health/color_blindness/facts_about|website=NEI|access-date=29 July 2016|date=February 2015|url-status=live|archive-url=https://web.archive.org/web/20160728003639/https://nei.nih.gov/health/color_blindness/facts_about|archive-date=28 July 2016))</ref>

<!-- Society and culture -->
Depending on the jurisdiction, the color blind are ineligible for certain careers,<ref name=Gor1998/> such as [[aircraft pilot]]s, [[train driver]]s, [[police officer]]s, [[firefighter]]s, and members of the [[armed forces]].<ref name=Gor1998/><ref>((Cite web|url=https://www.osha.gov/laws-regs/standardinterpretations/2004-01-29-0|title=OSHA does not have requirements for normal color vision. ((!)) Occupational Safety and Health Administration|website=www.osha.gov|access-date=2019-05-06))</ref> The effect of color blindness on artistic ability is controversial,<ref name=Gor1998/><ref>((cite journal | vauthors = Marmor MF, Lanthony P | title = The dilemma of color deficiency and art | journal = Survey of Ophthalmology | volume = 45 | issue = 5 | pages = 407–15 | date = March 2001 | pmid = 11274694 | doi = 10.1016/S0039-6257(00)00192-2 ))</ref> but a number of famous artists are believed to have been color blind.<ref name=Gor1998/><ref>((cite journal | vauthors = Marmor MF | title = Vision, eye disease, and art: 2015 Keeler Lecture | journal = Eye | volume = 30 | issue = 2 | pages = 287–303 | date = February 2016 | pmid = 26563659 | pmc = 4763116 | doi = 10.1038/eye.2015.197 ))</ref>

((TOC limit|4))

==Effects==
A color blind person will have decreased (or no) color discrimination along the red–green axis, blue–yellow axis, or both. However, the vast majority of the color blind are only affected on their red–green axis.

The first indication of color blindness generally consists of a person using the wrong color for an object, such as when painting, or calling a color by the wrong name. The colors that are confused are very consistent among people with the same type of color blindness.

<gallery>
File:Вечір на "інтегралі" - річка Південний Буг.jpg|Normal sight
File:Deuteranopia sight.jpg|Deuteranopic sight
File:Protanopia sight.png|Protanopic sight
File:Tritanopia sight.jpg|Tritanopic sight
File:Monochromacy sight.jpg|Monochromatic sight
</gallery>

===Confusion colors===
[[File:Color Blind Confusion Lines.png|thumb|upright=1.8|Confusion lines for the three types of dichromacy superimposed on CIEXYZ color space.]]
Confusion colors are pairs or groups of colors that will often be mistaken by the color blind. Confusion colors for red–green color blindness include:
* cyan and grey
* [[rose (color)|rose-pink]] and grey
* blue and purple
* yellow and [[Shades of green#Neon green|neon green]]
* red, green, orange, brown
Confusion colors for tritan include:
* yellow and grey
* blue and green
* dark blue/violet and black
* violet and yellow-green
* red and [[Rose (color)|rose-pink]]
These colors of confusion are defined quantitatively by straight confusion lines plotted in [[CIEXYZ]], usually plotted on the corresponding [[CIE 1931 color space#CIE xy chromaticity diagram and the CIE xyY color space|chromaticity diagram]]. The lines all intersect at a ''copunctal point'', which varies with the [[#Based on affected cone|type of color blindness]].<ref>((cite journal |last1=Fomins |first1=S |title=Multispectral analysis of color vision deficiency tests |journal=Materials Science |date=2011 |volume=17 |issue=1 |pages=104–108 |doi=10.5755/j01.ms.17.1.259|doi-access=free ))</ref> [[Chromaticity|Chromaticities]] along a confusion line will appear [[Metamerism (color)|metameric]] to [[#Dichromacy|dichromats]] of that type. [[#Anomalous trichromacy|Anomalous trichromats]] of that type will see the chromaticities as metameric if they are [[Color difference|close enough]], depending on the strength of their CVD. For two colors on a confusion line to be metameric, the chromaticities first have to be made ''isoluminant'', meaning equal in [[lightness]]. Also, colors that may be isoluminant to the [[CIE 1931 color space#CIE standard observer|standard observer]] may not be isoluminant to a person with dichromacy.

===Color tasks===
((main|Color task))
Cole describes four color tasks, all of which are impeded to some degree by color blindness:<ref>((cite journal |last1=Cole |first1=Barry L |title=The handicap of abnormal colour vision |journal=Clinical and Experimental Optometry |date=1972 |volume=55 |issue=8 |pages=304–310 |doi=10.1111/j.1444-0938.1972.tb06271.x))</ref>
* '''Comparative'''&nbsp;– When multiple colors must be compared, such as with mixing paint
* '''Connotative'''&nbsp;– When colors are given an implicit meaning, such as red = stop
* '''Denotative''' – When identifying colors, for example by name, such as "where is the yellow ball?"
* '''Aesthetic''' – When colors look nice – or convey an emotional response – but do not carry explicit meaning

The following sections describe specific color tasks with which the color blind typically have difficulty.

===Food===
[[File:Assorted Red and Green Apples (deuteranope view).jpg|thumb|Simulation of the normal (above) and dichromatic (below) perception of red and green apples]]
Color blindness causes difficulty with the ''connotative'' color tasks associated with selecting or preparing food. Selecting food for ripeness can be difficult; the green–yellow transition of bananas is particularly hard to identify. It can also be difficult to detect bruises, mold, or rot on some foods, to determine when meat is done by color, to distinguish some varietals, such as a [[Braeburn]] vs. a [[Granny Smith]] apple, or to distinguish colors associated with artificial flavors (e.g. jelly beans, sports drinks).

===Skin color===
((main|Evolution of color vision in primates#Skin Tone))
Changes in skin color due to bruising, sunburn, rashes or even blushing are easily missed by the red–green color blind.

===Traffic lights===
((See also|#Driving))
[[File:Salzburg - Gnigl - Eichstraße x Parscher Straße - 2020 01 03-2.jpg|thumb|The lack of standard positional clues makes this light difficult to interpret.]]
The colors of [[traffic light]]s can be difficult for the red–green color blindness. This difficulty includes distinguishing red/amber lights from sodium street lamps, distinguishing green lights (closer to cyan) from normal white lights, and distinguishing red from amber lights, especially when there are no positional clues available (see image).

[[File:Tipperary Hill - greenoverred Syracuse, New York.jpg|thumb|The infamous inverted traffic light in Syracuse, New York]]
The main coping mechanism to overcome these challenges is to memorize the position of lights. The order of the common triplet traffic light is standardized as red–amber–green from top to bottom or left to right. Cases that deviate from this standard are rare. One such case is a [[Tipperary Hill#Green over red|traffic light in Tipperary Hill]] in [[Syracuse, New York]], which is upside-down (green–amber–red top to bottom) due to the sentiments of its [[Irish American]] community.<ref>((cite news|title=New documentary uncovers the Irish links to America's Tipperary Hill|url=http://www.thejournal.ie/tipperary-hill-radio-documentary-3063059-Nov2016/|access-date=15 August 2017|agency=TheJournal.ie|date=6 November 2016|url-status=live|archive-url=https://web.archive.org/web/20170815182810/http://www.thejournal.ie/tipperary-hill-radio-documentary-3063059-Nov2016/|archive-date=15 August 2017))</ref> However, the light has been criticized due to the potential hazard it poses for color blind drivers.<ref>((cite web|url=https://gizmodo.com/the-story-behind-syracuses-upside-down-traffic-light-1545301615|title=The Story Behind Syracuse's Upside-Down Traffic Light|author=Zhang, Sarah|work=Gizmodo|date=17 March 2014 |url-status=live|archive-url=https://web.archive.org/web/20140916034424/http://gizmodo.com/the-story-behind-syracuses-upside-down-traffic-light-1545301615|archive-date=2014-09-16))</ref>

[[File:Colourblind traffic signal.JPG|thumb|Horizontal traffic light in [[Halifax, Nova Scotia]], Canada]]
There are other several features of traffic lights available that help accommodate the color blind. British Rail signals use more easily identifiable colors: The red is blood red, the amber is yellow and the green is a bluish color.((citation needed|date=June 2022)) Most British road traffic lights are mounted vertically on a black rectangle with a white border (forming a "sighting board"), so that drivers can more easily look for the position of the light. In the [[Eastern Canada|eastern provinces of Canada]], traffic lights are sometimes differentiated by shape in addition to color: square for red, diamond for yellow, and circle for green (see image).

===Signal lights===
((See also|#Occupations))
[[Navigation light]]s in marine and aviation settings employ red and green lights to signal the relative position of other ships or aircraft. [[Railway signal#Colour light signals|Railway signal lights]] also rely heavily on red–green–yellow colors. In both cases, these color combinations can be difficult for the red–green color blind. [[Farnsworth Lantern Test|Lantern Tests]] are a common means of simulating these light sources to determine not necessarily whether someone is color blind, but whether they can functionally distinguish these specific signal colors. Those who cannot pass this test are generally completely restricted from working on aircraft, ships or rail, for example.

===Fashion===
((see also|Color of clothing))
[[Color analysis]] is the analysis of color in its use in fashion, to determine personal color combinations that are most aesthetically pleasing.<ref>((Cite web |date=2022-01-01 |title=What is Color Analysis? |url=https://londonimageinstitute.com/what-is-color-analysis/ |access-date=2024-02-21 |website=London Image Institute |language=en-US))</ref> Colors to combine can include clothing, accessories, makeup, hair color, skin color, eye color, etc. Color analysis involves many aesthetic and comparative [[#Color tasks|color task]] that can be difficult for the color blind.

===Art===
Inability to distinguish color does not necessarily preclude the ability to become a celebrated artist. The 20th century expressionist painter [[Clifton Pugh]], three-time winner of Australia's [[Archibald Prize]], on biographical, gene inheritance and other grounds has been identified as a person with protanopia.<ref>((cite journal | vauthors = Cole BL, Harris RW | title = Colour blindness does not preclude fame as an artist: celebrated Australian artist Clifton Pugh was a protanope | journal = Clinical & Experimental Optometry | volume = 92 | issue = 5 | pages = 421–8 | date = September 2009 | pmid = 19515095 | doi = 10.1111/j.1444-0938.2009.00384.x | s2cid = 21676461 | doi-access = free ))</ref> 19th century French artist [[Charles Méryon]] became successful by concentrating on [[etching]] rather than painting after he was diagnosed as having a red–green deficiency.<ref>((cite encyclopedia|url=http://www.answers.com/topic/charles-m-ryon|title=Charles Meryon|last=Anon|encyclopedia=Art Encyclopedia. The Concise Grove Dictionary of Art.|publisher=Oxford University Press|access-date=7 January 2010|url-status=live|archive-url=https://web.archive.org/web/20101125063246/http://www.answers.com/topic/charles-m-ryon|archive-date=25 November 2010))</ref> [[Jin Kim (animator)|Jin Kim]]'s red–green color blindness did not stop him from becoming first an [[animator]] and later a character designer with [[Walt Disney Animation Studios]].<ref name="LeeHyoWon">((cite news |last1=Lee |first1=Hyo-won |title=Dreams come true, Disney style |url=http://www.koreatimes.co.kr/www/news/art/2014/01/135_87009.html |access-date=25 November 2019 |work=The Korea Times |date=15 May 2011))</ref>

===Advantages===
<!-- Will need to find a better place to put the information in this section -->
Deuteranomals are better at distinguishing shades of [[khaki]],<ref>((cite news | doi = 10.1038/news051205-1| title = Colour blindness may have hidden advantages| journal = Nature| date = December 5, 2005| last1 = Simonite| first1 = Tom ))</ref> which may be advantageous when looking for predators, food, or camouflaged objects hidden among foliage.<ref>((cite journal |last1=Bosten |first1=J.M. |last2=Robinson |first2=J.D. |last3=Jordan |first3=G. |last4=Mollon |first4=J.D. |title=Multidimensional scaling reveals a color dimension unique to 'color-deficient' observers |journal=Current Biology |date=December 2005 |volume=15 |issue=23 |pages=R950–R952 |doi=10.1016/j.cub.2005.11.031|pmid=16332521 |s2cid=6966946 |doi-access=free |bibcode=2005CBio...15.R950B ))</ref> Dichromats tend to learn to use texture and shape clues and so may be able to penetrate camouflage that has been designed to deceive individuals with normal color vision.<ref name="Morgan"/><ref>((cite journal | doi=10.1038/146226a0 | title=Colour-Blindness and Camouflage | journal=Nature | year=1940 | volume=146 | issue=3694 | page=226 | bibcode=1940Natur.146Q.226. | s2cid=4071103 | doi-access=free ))</ref>

Some tentative evidence finds that the color blind are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high rate of red–green color blindness.<ref name=Morgan>((cite journal | vauthors = Morgan MJ, Adam A, Mollon JD | s2cid = 35694740 | title = Dichromats detect colour-camouflaged objects that are not detected by trichromats | journal = Proceedings. Biological Sciences | volume = 248 | issue = 1323 | pages = 291–5 | date = June 1992 | pmid = 1354367 | doi = 10.1098/rspb.1992.0074 | bibcode = 1992RSPSB.248..291M ))</ref> There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision are not able to distinguish.<ref>((cite journal | vauthors = Bosten JM, Robinson JD, Jordan G, Mollon JD | title = Multidimensional scaling reveals a color dimension unique to 'color-deficient' observers | journal = Current Biology | volume = 15 | issue = 23 | pages = R950-2 | date = December 2005 | pmid = 16332521 | doi = 10.1016/j.cub.2005.11.031 | s2cid = 6966946 |url=http://sro.sussex.ac.uk/id/eprint/52520/4/Bosten05CurrentBiologyFinalAccepted.pdf | doi-access = free | bibcode = 2005CBio...15.R950B ))</ref> In World War II, color blind observers were used to penetrate camouflage.<ref>((cite news|title=Colour blindness not all it seems|url=http://news.bbc.co.uk/2/hi/health/4498734.stm|access-date=21 June 2016|work=[[BBC News]]|date=6 December 2015|url-status=live|archive-url=https://web.archive.org/web/20160623215610/http://news.bbc.co.uk/2/hi/health/4498734.stm|archive-date=23 June 2016))</ref>

In the presence of chromatic noise, the color blind are more capable of seeing a luminous signal, as long as the chromatic noise appears [[Metamerism (color)|metameric]] to them.<ref>((cite journal |last1=Sousa |first1=Bruna Rafaela Silva |last2=Loureiro |first2=Terezinha Medeiros Gonçalves |last3=Goulart |first3=Paulo Roney Kilpp |last4=Cortes |first4=Maria Izabel Tentes |last5=Costa |first5=Marcelo Fernandes |last6=Bonci |first6=Daniela Maria Oliveira |last7=Baran |first7=Luiz Claudio Portnoi |last8=Hauzman |first8=Einat |last9=Ventura |first9=Dora Fix |last10=Miquilini |first10=Leticia |last11=Souza |first11=Givago Silva |title=Specificity of the chromatic noise influence on the luminance contrast discrimination to the color vision phenotype |journal=Scientific Reports |date=21 October 2020 |volume=10 |issue=1 |pages=17897 |doi=10.1038/s41598-020-74875-3|pmid=33087826 |pmc=7578001 |bibcode=2020NatSR..1017897S ))</ref> This is the effect behind most "reverse" [[Pseudoisochromatic plate]]s (e.g. ''"hidden digit"'' [[Ishihara plate]]s) that are discernible to the color blind but unreadable to people with typical color vision.((citation needed|date=September 2022))

===Digital design===
((See also|Color coding in data visualization))
[[File:Safe Chart Colors-F99-FEC-ADD.jpg|thumb|alt=snippet of colored cells in a table (foreground), surrounded in background showing how the image appears in color-blindness simulations.|Testing the colors of a web chart, ''(center)'', to ensure that no information is lost to the various forms of color blindness.]]
[[Color code]]s are useful tools for designers to convey information. The interpretation of this information requires users to perform a variety of [[#Color tasks|Color Tasks]], usually comparative but also sometimes connotative or denotative. However, these tasks are often problematic for the color blind when design of the color code has not followed best practices for accessibility.<ref>((Cite journal |last=Hovis |first=Jeffery K. |date=July 2002 |title=Diagnosis of Defective Colour Vision, 2nd Ed. |url=https://journals.lww.com/optvissci/fulltext/2002/07000/diagnosis_of_defective_colour_vision,_2nd_ed__.5.aspx |journal=Optometry and Vision Science |language=en-US |volume=79 |issue=7 |pages=406 |doi=10.1097/00006324-200207000-00005 |issn=1538-9235|doi-access=free ))</ref> For example, one of the most ubiquitous [[#Color tasks|connotative]] color codes is the "red means bad and green means good" or similar systems, based on the classic [[#Signal lights|signal light colors]]. However, this color coding will almost always be [[#Confusion colors|undifferentiable]] to [[#Deutan|deutans]] or [[#Protan|protans]], and therefore should be avoided or supplemented with a parallel connotative system ([[Check mark|symbols]], [[smiley]]s, etc.).

Good practices to ensure design is accessible to the color blind include:
* When possible (e.g. in simple video games or apps), allowing the user to choose their own colors is the '''most''' inclusive design practice.
* Using other signals that are parallel to the color coding, such as patterns, shapes, size or order.<ref>((cite book|last1=Caprette|first1=Heather|title=Best Practices in Accessible Online Design|publisher=Pressbooks @ MSL|chapter=14 Avoiding the Use of Color Alone to Convey Meaning and Algorithms That Help|chapter-url=https://pressbooks.ulib.csuohio.edu/accessibility/chapter/chapter-2-3-avoiding-the-use-of-color-alone-to-convey-meaning-and-algorithms-that-help/))</ref> This not only helps the color blind, but also aids understanding by normally sighted people by providing them with multiple reinforcing cues.
* Using brightness contrast (different shades) in addition to color contrast (different hues)
* To achieve good contrast, conventional wisdom suggests [[Color coding in data visualization#Grayscale, an important tool for visualization of data|converting a (digital) design to grayscale]] to ensure there is sufficient brightness contrast between colors. However, this does not account for the [[Luminous efficiency function#Color blindness|different perceptions of brightness to different varieties of color blindness]], especially [[#Protan|protan]] CVD, [[#Tritan|tritan]] CVD and [[#Monochromacy|monochromacy]].
* Viewing the design through a '''CVD Simulator''' to ensure the information carried by color is still sufficiently conveyed. At a minimum, the design should be tested for [[#Deutan|deutan]] CVD, the most common kind of color blindness.
* Maximizing the area of colors (e.g. increase size, thickness or boldness of colored element) makes the color easier to identify. [[Color coding in data visualization#Symbol size affects color salience|Color contrast improves as the angle the color subtends on the retina increases]]. This applies to all types of color vision.
* Maximizing brightness (value) and saturation (chroma) of the colors to maximize color contrast.
* Converting connotative tasks to comparative tasks by including a [[Chart#Features|legend]], even when the meaning is considered obvious (e.g. [[Red#Warning and danger|red means danger]]).
* Avoiding denotative color tasks ([[Color term|color naming]]) when possible. Some denotative tasks can be converted to comparative tasks by depicting the actual color whenever the color name is mentioned; for example, colored typography in "((font color|purple|'''purple'''))", ((color box|Purple|purple)) or "purple (((Color sample|purple)))". 
* For denotative tasks ([[Color term|color naming]]), using the most common shades of colors. For example, green and yellow are colors of confusion in red–green CVD, but it is very common to mix forest green (((Color sample|green))) with bright yellow (((Color sample|yellow))). Mistakes by the color blind increase drastically when uncommon shades are used, e.g. neon green (((Color sample|#0F5))) with dark yellow (((Color sample|#882))).
* For denotative tasks, using colors that are classically associated with a color name. For example, use "firetruck" red (((Color sample|red))) instead of [[Burgundy (color)|burgundy]] (((Color sample|#802))) to represent the word "[[red]]".

====Unordered Information====
[[File:Delivery track of the board game Great Western Trail.jpg|thumb|Colors of [[board game]] pieces must be carefully chosen to be accessible to the color blind]]

A common task for designers is to select a subset of colors (''qualitative'' colormap) that are as mutually differentiable as possible ([[Color coding in data visualization#Choosing salient colors for color coding|salient]]). For example, player pieces in a [[board game]] should be as different as possible.

Classic advice suggests using [[Cynthia Brewer#Brewer palettes|Brewer palettes]], but several of these are ''not'' actually accessible to the color blind.

Unfortunately, the colors with the greatest [[Contrast (vision)|contrast]] to the [[#Red–green color blindness|red–green color blind]] tend to be [[#Confusion colors|colors of confusion]] to the [[#Blue–yellow color blindness|blue–yellow color blind]], and vice versa. However, since red–green is much [[#Epidemiology|more prevalent]] than blue–yellow CVD, design should((According to whom|date=July 2023)) generally prioritize those users ([[#Deutan|deutans]] then [[#Protan|protans]]).

====Ordered Information====
[[File:CVD-friendly sequential colormaps.png|thumb|left|Three sequential colormaps that have been designed to be accessible to the color blind.]]

A common task for data visualization is to represent a color scale, or ''sequential'' colormap, often in the form of a [[heat map]] or [[choropleth]]. Several scales are designed with special consideration for the color blind and are widespread in academia, including Cividis,<ref name=VIRIDIS/> Viridis<ref name="VIRIDIS">((cite journal |last1=Nuñez |first1=JR |date=2018 |title=Optimizing colormaps with consideration for color vision deficiency to enable accurate interpretation of scientific data |journal=PLOS ONE |volume=13 |issue=7 |pages=e0199239 |doi=10.1371/journal.pone.0199239 |pmid=30067751 |pmc=6070163 |arxiv=1712.01662 |bibcode=2018PLoSO..1399239N |access-date=|doi-access=free ))</ref> and [[Parula#In art|Parula]]. These comprise a light-to-dark scale superimposed on a yellow-to-blue scale, making them [[monotonic]] and perceptually uniform to all forms of color vision.

==Classification==
[[File:Color blindness.svg|thumb|upright=1.5|These color charts show how different color blind people see compared to a person with normal color vision.((Dubious|date=March 2023))]]
Much terminology has existed and does exist for the classification of color blindness, but the typical classification for color blindness follows the von Kries classifications,<ref>((cite journal |last1=von Kries |first1=J. |date=1897 |title=Ueber Farbensysteme |journal=Zeitschrift für Psychologie Physiologie Sinnesorg |volume=13 |pages=241–324))</ref> which uses severity and affected cone for naming.

===Based on severity===
Based on clinical appearance, color blindness may be described as total or partial. Total color blindness (monochromacy) is much less common than partial color blindness.<ref>((cite web |url=http://micro.magnet.fsu.edu/primer/lightandcolor/humanvisionhome.html |title=Human Vision and Color Perception |publisher=[[Florida State University]] |last1=Spring |first1=Kenneth R. |first2=Matthew J. |last2=Parry-Hill |first3=Thomas J. |last3=Fellers |first4=Michael W. |last4=Davidson |access-date=2007-04-05 |url-status=live |archive-url=https://web.archive.org/web/20070827191749/http://micro.magnet.fsu.edu/primer/lightandcolor/humanvisionhome.html |archive-date=2007-08-27 ))</ref>  Partial color blindness includes dichromacy and anomalous trichromacy, but is often clinically defined as mild, moderate or strong.

====Monochromacy====
((Main|Monochromacy))
Monochromacy is often called ''total color blindness'' since there is no ability to see color. Although the term may refer to acquired disorders such as [[cerebral achromatopsia]], it typically refers to congenital color vision disorders, namely [[Achromatopsia|rod monochromacy]] and [[blue cone monochromacy]]).<ref name=":0">((cite web|url=http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/|title=Types of Colour Blindness|work=Colour Blind Awareness|url-status=live|archive-url=https://web.archive.org/web/20140529052207/http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/|archive-date=2014-05-29))</ref><ref name=blom>
((cite book |title       = A Dictionary of Hallucinations |first       = Jan Dirk |last        = Blom |publisher   = Springer |year        = 2009 |isbn        = 978-1-4419-1222-0 |page        = 4 |url=https://books.google.com/books?id=KJtQptBcZloC&pg=PA4 |url-status     = live |archive-url  = https://web.archive.org/web/20161227164302/https://books.google.com/books?id=KJtQptBcZloC&pg=PA4 |archive-date = 2016-12-27 ))</ref>

In cerebral achromatopsia, a person cannot perceive colors even though the eyes are capable of distinguishing them. Some sources do not consider these to be true color blindness, because the failure is of perception, not of vision. They are forms of [[visual agnosia]].<ref name=blom/>

[[Monochromacy]] is the condition of possessing only a single channel for conveying information about color. Monochromats are unable to distinguish any colors and perceive only variations in brightness. Congenital monochromacy occurs in two primary forms:
# Rod monochromacy, frequently called complete [[achromatopsia]], where the retina contains no cone cells, so that in addition to the absence of color discrimination, vision in lights of normal intensity is difficult.
# Cone monochromacy is the condition of having only a single class of cone. A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues. Cone monochromacy is divided into classes defined by the single remaining cone class. However, red and green cone monochromats have not been definitively described in the literature. [[Blue cone monochromacy]] is caused by lack of functionality of L (red) and M (green) cones, and is therefore mediated by the same genes as red–green color blindness (on the X chromosome). Peak spectral sensitivities are in the blue region of the visible spectrum (near 440&nbsp;nm). People with this condition generally show [[nystagmus]] ("jiggling eyes"), [[photophobia]] (light sensitivity), reduced [[visual acuity]], and [[myopia]] (nearsightedness).<ref>((cite journal | vauthors = Weiss AH, Biersdorf WR | title = Blue cone monochromatism | journal = Journal of Pediatric Ophthalmology and Strabismus | volume = 26 | issue = 5 | pages = 218–23 | year = 1989 | doi = 10.3928/0191-3913-19890901-04 | pmid = 2795409 | s2cid = 23037026 ))</ref> Visual acuity usually falls to the 20/50 to 20/400 range.

====Dichromacy====
((main|Dichromacy))
Dichromats can match any color they see with some mixture of just two [[primary color]]s (in contrast to those with normal sight ([[Trichromacy|trichromats]]) who can distinguish three primary colors).<ref name=":0" /> Dichromats usually know they have a color vision problem, and it can affect their daily lives. Dichromacy in humans includes protanopia, deuteranopia, and tritanopia. Out of the male population, 2% have severe difficulties distinguishing between red, orange, yellow, and green (orange and yellow are different combinations of red and green light). Colors in this range, which appear very different to a normal viewer, appear to a dichromat to be the same or a similar color. The terms protanopia, deuteranopia, and tritanopia come from Greek, and respectively mean "inability to see (''anopia'') with the first (''prot-''), second (''deuter-''), or third (''trit-'') [cone]".

====Anomalous trichromacy====
Anomalous trichromacy is the mildest type of color deficiency, but the severity ranges from almost dichromacy (strong) to almost normal trichromacy (mild).<ref>((cite journal | vauthors = Simunovic MP | title = Colour vision deficiency | journal = Eye | volume = 24 | issue = 5 | pages = 747–55 | date = May 2010 | pmid = 19927164 | doi = 10.1038/eye.2009.251 | doi-access = free ))</ref> In fact, many mild anomalous trichromats have very little difficulty carrying out tasks that require normal color vision and some may not even be aware that they have a color vision deficiency. The types of anomalous trichromacy include protanomaly, deuteranomaly and tritanomaly.  It is approximately three times more common than [[dichromacy]].<ref>((Cite journal |doi=10.1016/j.gde.2006.04.002|title=Genetics of variation in human color vision and the retinal cone mosaic|year=2006|last1=Deeb|first1=Samir S.|journal=Current Opinion in Genetics & Development|volume=16|issue=3|pages=301–307|pmid=16647849))</ref> Anomalous trichromats exhibit [[trichromacy]], but the color matches they make differ from normal trichromats. In order to match a given spectral yellow light, protanomalous observers need more red light in a red/green mixture than a normal observer, and deuteranomalous observers need more green. This difference can be measured by an instrument called an [[Anomaloscope]], where red and green lights are mixed by a subject to match a yellow light.<ref>((cite journal|doi=10.1016/0042-6989(79)90209-8|title=Optimization of a Rayleigh-type equation for the detection of tritanomaly|year=1979|last1=Moreland|first1=J.D.|last2=Kerr|first2=J.|journal=Vision Research|volume=19|issue=12|pages=1369–1375|pmid=316945|s2cid=29379397 ))</ref>

===Based on affected cone===
There are two major types of color blindness: difficulty distinguishing between red and green, and difficulty distinguishing between blue and yellow.<ref>((cite web|url=http://www.digitalspaceart.com/articles/ColorBlindness.pdf |title=Accommodating Color Blindness |first=Paul S. |last=Hoffman |access-date=2009-07-01 |url-status=dead |archive-url=https://web.archive.org/web/20080515103432/http://www.digitalspaceart.com/articles/ColorBlindness.pdf |archive-date=15 May 2008 ))</ref><ref>((cite web|url=http://healthlink.mcw.edu/article/999211295.html |title=Severity of Colorblindness Varies |last=Neitz |first=Maureen E. |author-link= Maureen Neitz |publisher=[[Medical College of Wisconsin]] |access-date=2007-04-05 |url-status=dead |archive-url=https://web.archive.org/web/20070205055320/http://healthlink.mcw.edu/article/999211295.html |archive-date=5 February 2007 ))</ref>((Dubious |Tritanopia|date=September 2020)) These definitions are based on the [[phenotype]] of the partial color blindness. Clinically, it is more common to use a genotypical definition, which describes which [[cone cell|cone]]/[[opsin]] is affected.

====Red–green color blindness====
Red–green color blindness includes '''protan''' and '''deutan''' CVD. Protan CVD is related to the L-cone and includes protanomaly (anomalous trichromacy) and protanopia (dichromacy). Deutan CVD is related to the M-cone and includes deuteranomaly (anomalous trichromacy) and deuteranopia (dichromacy).<ref name=pmid21774112>
((cite journal
 | last = Wong |first = B.
 | date = June 2011
 | title = Color blindness
 | journal = Nature Methods
 | volume = 8 | issue = 6 | pages = 441
 | s2cid = 36690778 | pmid = 21774112
 | doi = 10.1038/nmeth.1618
))
</ref><ref>((cite journal | vauthors = Neitz J, Neitz M | title = The genetics of normal and defective color vision | journal = Vision Research | volume = 51 | issue = 7 | pages = 633–51 | date = April 2011 | pmid = 21167193 | pmc = 3075382 | doi = 10.1016/j.visres.2010.12.002 ))</ref> The phenotype (visual experience) of deutans and protans is quite similar. Common colors of confusion include red/brown/green/yellow as well as blue/purple. Both forms are almost always symptomatic of [[congenital red–green color blindness]], so affects males disproportionately more than females.<ref name=harrison>((cite book|last1=Harrison|first1=G.A.|last2=Tanner|first2=J.M.|last3=Pilbeam|first3=D.R.|last4=Baker|first4=P.T.|title=Human Biology|pages=[https://archive.org/details/humanbiologyintr00gaha/page/183 183–187, 287–290]|location=Oxford|publisher=Oxford University Press|date=1988|isbn=978-0-19-854144-8|url=https://archive.org/details/humanbiologyintr00gaha/page/183))</ref> This form of color blindness is sometimes referred to as ''daltonism'' after [[John Dalton (scientist)|John Dalton]], who had red–green dichromacy. In some languages, ''daltonism'' is still used to describe red–green color blindness.

[[File:ConeMosaics.jpg|thumb|upright=1.4|Illustration of the distribution of cone cells in the [[Fovea centralis|fovea]] of an individual with normal color vision (left), and a color blind (protanopic) retina. The center of the fovea holds very few blue-sensitive cones.]]
((anchor|Protanopia))
((anchor|Protanomaly))
((anchor|Protan))
* '''Protan''' (2% of males): Lacking, or possessing anomalous [[OPN1LW|L-opsins]] for long-wavelength sensitive cone cells. Protans have a neutral point at a [[cyan]]-like wavelength around 492&nbsp;nm (see [[spectral color]] for comparison)—that is, they cannot discriminate light of this wavelength from [[white]]. For a protanope, the brightness of red, is much reduced compared to normal.<ref name="Genetics">((cite journal|last1=Neitz|first1=Jay|first2=Maureen|last2=Neitz|title=The genetics of normal and defective color vision|journal=Vision Research|volume=51|issue=7|date=2011|pages=633–651| doi=10.1016/j.visres.2010.12.002|pmid=21167193|pmc=3075382))</ref> This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. [[shades of violet|Violet]], [[shades of purple|lavender, and purple]] are indistinguishable from various [[shades of blue]]. A very few people have been found who have one normal eye and one protanopic eye. These ''unilateral dichromats'' report that with only their protanopic eye open, they see wavelengths shorter than neutral point as blue and those longer than it as yellow.
((anchor|Deuteranopia))
((anchor|Deuteranomaly))
((anchor|Deutan))
* '''Deutan''' (6% of males): Lacking, or possessing anomalous [[OPN1MW|M-opsin]]s for medium-wavelength sensitive cone cells. Their neutral point is at a slightly longer wavelength, 498&nbsp;nm, a more greenish hue of cyan. Deutans have the same hue discrimination problems as protans, but without the dimming of long wavelengths. Deuteranopic unilateral dichromats report that with only their deuteranopic eye open, they see wavelengths shorter than neutral point as blue and longer than it as yellow.<ref>((cite book |title= Contributions to color science |editor1-last= MacAdam |editor1-first=David L. |editor2-last=Judd |editor2-first=Deane B. |publisher=NBS |year=1979 |page=584 |url=https://books.google.com/books?id=jgz_iI8NAzYC&pg=PA584))</ref>

====Blue–yellow color blindness====
Blue–yellow color blindness includes '''tritan''' CVD. Tritan CVD is related to the S-cone and includes tritanomaly (anomalous trichromacy) and tritanopia (dichromacy). Blue–yellow color blindness is much less common than red–green color blindness, and more often has acquired causes than genetic. Tritans have difficulty discerning between bluish and greenish hues.<ref>Steefel, Lorraine T., and Timothy E. Moore, PhD. "Color Blindness." ''The Gale Encyclopedia of Nursing and Allied Health'', edited by Jacqueline L. Longe, 4th ed., vol. 2, Gale, 2018, pp. 890–892. ''Gale eBooks'', Accessed 29 Dec. 2021.</ref> Tritans have a neutral point at 571&nbsp;nm (yellowish).((citation needed|date=June 2022))

((anchor|Tritanopia))
((anchor|Tritanomaly))
((anchor|Tritan))
* '''Tritan''' (<&nbsp;0.01% of individuals): Lacking, or possessing anomalous [[OPN1SW|S-opsins]] or short-wavelength sensitive cone cells. Tritans see short-wavelength colors ([[blue]], [[indigo]] and spectral [[Violet (color)|violet]]) as greenish and drastically dimmed, some of these colors even as [[black]]. Yellow and orange are indistinguishable from [[white]] and [[pink]] respectively, and purple colors are perceived as various [[shades of red]]. Unlike protans and deutans, the mutation for this color blindness is carried on chromosome 7. Therefore, it is not sex-linked (equally prevalent in both males and females). The OMIM gene code for this mutation is 304000 "Colorblindness, Partial Tritanomaly".<ref>((cite web | title = Disease-causing Mutations and protein structure |url=http://www.biochem.ucl.ac.uk/bsm/humgen/chr__034.html#304000 | archive-url=https://web.archive.org/web/20050501081119/http://www.biochem.ucl.ac.uk/bsm/humgen/chr__034.html#304000 | url-status = dead | archive-date = 2005-05-01 | publisher = UCL Biochemistry BSM Group | access-date = 2007-04-02 ))</ref>
((anchor|Tetartanopia))
((anchor|Tetartanomaly))
((anchor|Tetartan))
* '''Tetartan''' is the "fourth type" of color blindness, and a type of blue–yellow color blindness. However, its existence is hypothetical and given the molecular basis of human color vision, it is unlikely this type could exist.((citation needed|date=June 2022))

===Summary of cone complements===
The below table shows the cone complements for different types of human color vision, including those considered color blindness, normal color vision and 'superior' color vision. The cone complement contains the types of cones (or their opsins) expressed by an individual.
{|class="wikitable"
|- style="background:#eaecf0;color:#000000;"
|colspan="2" rowspan="2" style="text-align:right; vertical-align:top;"|Cone system
|colspan="2"|Red  ||rowspan="13" style="font-size:1px;"|
|colspan="2"|Green||rowspan="13" style="font-size:1px;"|
|colspan="2"|Blue
|colspan="3" rowspan="2" style="vertical-align:bottom;"|'''N'''&nbsp;=&nbsp;normal<br />'''A'''&nbsp;=&nbsp;anomalous
|- style="background:#eaecf0;color:#000000;"
|'''N'''||'''A'''||'''N'''||'''A'''||'''N'''||'''A'''
|-
|style="text-align:right;"|1||Normal vision
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|Trichromacy||colspan="2"|Normal
|- style="border-top:double #a2a9b1;"
|style="text-align:right;"|2||Protanomaly
|style="background:#000000"| ||style="background:#FF0000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|Anomalous trichromacy
|rowspan="6"|Partial<br />color<br />blindness||rowspan="4"|Red–<br />green
|-
|style="text-align:right;"|3||Protanopia
|style="background:#000000"| ||style="background:#000000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|Dichromacy
|- style="border-top:2px solid #a2a9b1;"
|style="text-align:right;"|4||Deuteranomaly
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#00FF00"|
|style="background:#0000FF"| ||style="background:#000000"|
|Anomalous trichromacy
|-
|style="text-align:right;"|5||Deuteranopia
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|Dichromacy
|- style="border-top:2px solid #a2a9b1;"
|style="text-align:right;"|6||Tritanomaly
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#0000FF"|
|Anomalous trichromacy||rowspan="2"|Blue–<br />yellow
|-
|style="text-align:right;"|7||Tritanopia
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#000000"|
|Dichromacy
|- style="border-top:double #a2a9b1;"
|style="text-align:right;"|8||Blue cone monochromacy
|style="background:#000000"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|rowspan="2"|Monochromacy
|colspan="2" rowspan="2"|Total color blindness
|-
|style="text-align:right;"|9||Achromatopsia
|style="background:#000000"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#000000"|
|style="background:#000000"| ||style="background:#000000"|
|- style="border-top:double #a2a9b1;"
|style="text-align:right;"|10||rowspan="2"|Tetrachromacy<br />(carrier theory)
|style="background:#FF0000"| ||style="background:#FF0000"|
|style="background:#00FF00"| ||style="background:#000000"|
|style="background:#0000FF"| ||style="background:#000000"|
|rowspan="2"|Tetrachromacy
|colspan="2"  rowspan="2"|'Superior'
|-
|style="text-align:right;"|11
|style="background:#FF0000"| ||style="background:#000000"|
|style="background:#00FF00"| ||style="background:#00FF00"|
|style="background:#0000FF"| ||style="background:#000000"|
|}

==Causes==
((See also|Trichromatic color vision|Congenital red–green color blindness#Mechanism))
Color blindness is any deviation of color vision from normal [[trichromatic]] color vision (often as defined by the [[CIE 1931 color space#CIE standard observer|standard observer]]) that produces a reduced [[gamut]]. Mechanisms for color blindness are related to the functionality of [[cone cell]]s, and often to the expression of [[photopsin]]s, the [[photopigments]] that 'catch' [[photons]] and thereby convert light into chemical signals.

Color vision deficiencies can be classified as inherited or acquired.
* ''Inherited'': inherited or congenital/genetic color vision deficiencies are most commonly caused by mutations of the  genes encoding opsin proteins. However, several other genes can also lead to less common and/or more severe forms of color blindness.
* ''Acquired'': color blindness that is not present at birth, may be caused by chronic illness, accidents, medication, chemical exposure or simply normal aging processes.<ref>
((cite web
 |title=Acquired colour vision defects
 |website=colourblindawareness.org
 |url=http://www.colourblindawareness.org/colour-blindness/acquired-colour-vision-defects/
 |archive-url=https://web.archive.org/web/20141216094549/http://www.colourblindawareness.org/colour-blindness/acquired-colour-vision-defects/
 |archive-date=2014-12-16
))
</ref>

===Genetics===
((unreferenced section|date=May 2023))

Color blindness is typically an inherited genetic disorder. The most common forms of color blindness are associated with the [[Photopsin]] genes, but the mapping of the human genome has shown there are many causative mutations that do not directly affect the opsins. Mutations capable of causing color blindness originate from at least 19&nbsp;different chromosomes and 56&nbsp;different genes (as shown online at the [[Online Mendelian Inheritance in Man]] [OMIM]).

====Genetics of red–green color blindness====
((main|Congenital red–green color blindness#Genetics))
[[File:Punnett square colour blindness.svg|thumb|alt=A chart showing likelihoods of genetic combinations and outcomes for red–green color blindness|Punnett squares for each combination of parents' color vision status giving probabilities of their offsprings' status; A superscript 'c' denotes a chromosome with an affected gene]]
By far the most common form of color blindness is [[congenital red–green color blindness]] (Daltonism), which includes protanopia/protanomaly and deuteranopia/deuteranomaly. These conditions are mediated by the [[OPN1LW]] and [[OPN1MW]] genes, respectively, both on the [[X chromosome]]. An 'affected' gene is either missing (as in Protanopia and Deuteranopia - [[Dichromacy]]) or is a [[chimeric gene]] (as in Protanomaly and Deuteranomaly).

Since the [[OPN1LW]] and [[OPN1MW]] genes are on the X&nbsp;chromosome, they are [[Sex linkage|sex-linked]], and therefore affect males and females disproportionately. Because the color blind 'affected' [[alleles]] are recessive, color blindness specifically follows [[X-linked recessive inheritance]]. Males have only one X&nbsp;chromosome (XY), and females have two (XX); Because the male only has one of each gene, if it is affected, the male will be color blind. Because a female has two alleles of each gene (one on each chromosome), if only one gene is affected, the dominant normal alleles will "override" the affected, recessive allele and the female will have normal color vision. However, if the female has two mutated alleles, she will still be color blind. This is why there is a disproportionate prevalence of color blindness, with ~8% of males exhibiting color blindness and ~0.5% of females.

====Genetics of blue–yellow color blindness====
Congenital blue–yellow color blindness is a much rarer form of color blindness including tritanopia/tritanomaly. These conditions are mediated by the [[OPN1SW]] gene on [[Chromosome 7]] which encodes the S-opsin protein and follows autosomal dominant inheritance.<ref name="Sharpe1999"/> The cause of blue–yellow color blindness is not analogous to the cause of red–green color blindness, i.e. the peak sensitivity of the S-opsin does not shift to longer wavelengths. Rather, there are 6 known point mutations of OPN1SW that degrade the performance of the S-cones.<ref name="RCM2020">((cite book |last1=Rodriguez-Carmona |first1=Marisa |last2=Patterson |first2=Emily J. |chapter=Photoreceptors, Color Vision |title=Encyclopedia of Color Science and Technology |date=2020 |pages=1–7 |doi=10.1007/978-3-642-27851-8_277-3|isbn=978-3-642-27851-8 |s2cid=226504635 |chapter-url=https://openaccess.city.ac.uk/id/eprint/23584/1/Photoreceptors%20Color%20Vision_submitted%20to%20CRO.pdf ))</ref> The OPN1SW gene is almost invariant in the human population. Congenital tritan defects are often progressive, with nearly normal trichromatic vision in childhood (e.g. mild tritanomaly) progressing to dichromacy (tritanopia) as the S-cones slowly die.<ref name="RCM2020"/> Tritanomaly and tritanopia are therefore different penetrance of the same disease, and some sources have argued that tritanomaly therefore be referred to as incomplete tritanopia.<ref name="Sharpe1999">((cite book |last1=Sharpe |first1=LT |last2=Stockman |first2=A |last3=Jägle |first3=H |last4=Nathans |first4=J |title=Color vision: From genes to perception |date=1999 |page=351 |url=http://www.cvrl.org/people/stockman/pubs/1999%20Genetics%20chapter%20SSJN.pdf |chapter=Opsin genes, cone photopigments, color vision, and color blindness. |quote=True cases of tritanomaly, as distinct from partial or incomplete tritanopia, have never been satisfactorily documented. Although the separate existence of tritanopia and tritanomaly, with different modes of inheritance, has been postulated, it now seems more likely that tritanomaly does not exist, but rather has been mistaken for incomplete tritanopia.))</ref>

====Other genetic causes====
Several inherited diseases are known to cause color blindness, including [[achromatopsia]], [[cone dystrophy]], [[Leber's congenital amaurosis]] and [[retinitis pigmentosa]]. These can be [[congenital]] or commence in childhood or adulthood. They can be static/stationary or [[Progressive disease|progressive]]. Progressive diseases often involve deterioration of the retina and other parts of the eye, so often progress from color blindness to more severe [[visual impairment]]s, up to and including total blindness.

===Non-genetic causes===
Physical trauma can cause color blindness, either neurologically – brain trauma which produces swelling of the brain in the [[occiput|occipital lobe]] – or retinally, either acute (e.g. from laser exposure) or chronic (e.g. from [[ultraviolet light]] exposure).

Color blindness may also present itself as a symptom of degenerative diseases of the eye, such as [[cataract]] and age-related [[macular degeneration]], and as part of the retinal damage caused by [[diabetes]]. [[Vitamin A]] deficiency may also cause color blindness.<ref>
((cite book
 |editor1-last=Leikin  |editor1-first=Jerrold B.
 |editor2-last=Lipsky  |editor2-first=Martin S.
 |year=2003
 |title=Complete Medical Encyclopedia  |edition=First
 |page=[https://archive.org/details/americanmedicala00amer/page/388 388]
 |publisher=Random House, for the American Medical Association
 |location=New York, NY
 |series=Random House Reference
 |isbn=978-0-8129-9100-0
 |via=archive.org
 |url=https://archive.org/details/americanmedicala00amer
 |access-date=1 December 2011 |url-access=registration
))
</ref>

Color blindness may be a [[side effect]] of prescription drug use. For example, red–green color blindness can be caused by [[ethambutol]], a drug used in the treatment of [[tuberculosis]].<ref>
((cite web
 |title=Myambutol (Ethambutol)
 |series=drug information
 |website=RxList.com
 |quote=Description, user reviews, drug side effects, interactions–prescribing information
 |url=http://www.rxlist.com/myambutol-drug.htm
 |access-date=2014-05-24  |url-status=live
 |archive-url=https://web.archive.org/web/20140708223716/http://www.rxlist.com/myambutol-drug.htm
 |archive-date=2014-07-08
))
</ref> Blue–yellow color blindness can be caused by [[sildenafil]], an active component of [[Viagra]].<ref>
((cite web
 |title=VIAGRA (SILDENAFIL CITRATE) DRUG
 |series=drug information
 |website=RxList.com
 |quote=Description, user reviews, drug side effects, interactions–prescribing information
 |url=http://www.rxlist.com/viagra-drug.htm
 |access-date=2022-06-03
))
</ref> [[Hydroxychloroquine]] can also lead to hydroxychloroquine retinopathy, which includes various color defects.<ref>
((cite book
 |last1=Fraunfelder |first1=Frederick T.
 |last2=Fraunfelder |first2=Frederick W.
 |last3=Chambers |first3=Wiley A.
 |year=2014
 |title=Drug-Induced Ocular Side Effects: Clinical ocular toxicology e‑book
 |page=79
 |publisher=Elsevier Health Sciences
 |isbn=978-0-323-31985-0
 |url=https://books.google.com/books?id=6bqXBAAAQBAJ&pg=PA79
 |language=en
))
</ref> Exposure to chemicals such as styrene<ref>
((cite journal
 |vauthors = Choi AR, Braun JM, Papandonatos GD, Greenberg PB
 |date = November 2017
 |title = Occupational styrene exposure and acquired dyschromatopsia: A systematic review and meta-analysis
 |journal = American Journal of Industrial Medicine
 |volume = 60 |issue = 11 |pages = 930–946
 |pmid = 28836685 |pmc = 5652067
 |doi = 10.1002/ajim.22766
))
</ref> or organic solvents<ref>
((cite journal
 |vauthors = Betancur-Sánchez AM, Vásquez-Trespalacios EM, Sardi-Correa C
 |date = January 2017
 |title = Impaired colour vision in workers exposed to organic solvents: A systematic review
 |journal = Archivos de la Sociedad Espanola de Oftalmologia
 |volume = 92 |issue = 1 |pages = 12–18
 |pmid = 27422480 |doi = 10.1016/j.oftal.2016.05.008
))
</ref><ref name="Dick">
((cite journal
 | last = Dick  |first = F.D.
 | date = March 2006
 | title = Solvent neurotoxicity
 | journal = Occupational and Environmental Medicine
 | volume = 63 | issue = 3 | pages = 221–6, 179
 | pmid = 16497867 | pmc = 2078137 | doi = 10.1136/oem.2005.022400
))
</ref> can also lead to color vision defects.

Simple colored filters can also create mild color vision deficiencies. John Dalton's original hypothesis for his deuteranopia was actually that the [[vitreous humor]] of his eye was discolored:

((Blockquote
|text=I was led to conjecture that one of the humours of my eye must be a transparent, but coloured, medium, so constituted as to absorb red and green rays principally... I suppose it must be the vitreous humor.
|author=John Dalton
|source=''Extraordinary facts relating to the vision of colours: with observations'' (1798)
))

An autopsy of his eye after his death in 1844 showed this to be definitively untrue,<ref>((cite journal |last1=Hunt |first1=D. |last2=Dulai |first2=K. |last3=Bowmaker |first3=J. |last4=Mollon |first4=J. |title=The Chemistry of John Dalton's Color Blindness |journal=Science |date=February 17, 1995 |volume=267 |issue=5200 |pages=984–988 |doi=10.1126/science.7863342|pmid=7863342 |bibcode=1995Sci...267..984H |s2cid=6764146 ))</ref> though other filters are possible. Actual physiological examples usually affect the blue–yellow opponent channel and are named [[Cyanopsia]] and [[Xanthopsia]], and are most typically an effect of yellowing or removal of the [[Lens (anatomy)|lens]].

The opponent channels can also be affected by the prevalence of certain cones in the [[retinal mosaic]]. The cones are not equally prevalent and not evenly distributed in the retina. When the number of one of these cone types is significantly reduced, this can also lead to or contribute to a color vision deficiency. This is one of the causes of '''tritanomaly'''.

Some people are also unable to distinct between blue and green, which appears to be a combination of [[Cultural neuroscience#Culture differences in visual stimuli|culture]] and exposure to UV-light.<ref>[https://www.nature.com/articles/s41598-021-98550-3 Environment and culture shape both the colour lexicon and the genetics of colour perception]</ref>

==Diagnosis==
===Color vision test===
((main|Color vision test))
[[Image:Ishihara compare 1.jpg|right|thumb|upright=1.4|An Ishihara test image as seen by subjects with normal color vision and by those with a variety of color deficiencies]]
The main method for diagnosing a color vision deficiency is in testing the color vision directly. The [[Ishihara color test]] is the test most often used to detect red–green deficiencies and most often recognized by the public.<ref name="Gor1998"/> Some tests are clinical in nature, designed to be fast, simple, and effective at identifying broad categories of color blindness. Others focus on precision and are generally available only in academic settings.<ref>((cite journal | vauthors = Toufeeq A | title = Specifying colours for colour vision testing using computer graphics | journal = Eye | volume = 18 | issue = 10 | pages = 1001–5 | date = October 2004 | pmid = 15192692 | doi = 10.1038/sj.eye.6701378 | doi-access = free ))</ref>
* '''Pseudoisochromatic plates''', a classification which includes the [[Ishihara color test]] and HRR test, embed a figure in the plate as a number of spots surrounded by spots of a slightly different color. These colors must appear identical ([[Metamerism (color)|metameric]]) to the color blind but distinguishable to color normals. Pseudoisochromatic plates are used as screening tools because they are cheap, fast, and simple, but they do not provide precise diagnosis of CVD.
* '''Lanterns''', such as the [[Farnsworth Lantern Test]], project small colored lights to a subject, who is required to identify the color of the lights. The colors are those of typical signal lights, i.e. red, green, and yellow, which also happen to be colors of confusion of red–green CVD. Lanterns do not diagnose color blindness, but they are occupational screening tests to ensure an applicant has sufficient color discrimination to be able to perform a job.
[[Image:Huetestfmd15-2.jpg|right|thumb|upright=1.4|A Farnsworth D-15 test]]
* '''Arrangement tests''' can be used as screening or diagnostic tools. The [[Farnsworth–Munsell 100 hue test#100 hue test|Farnsworth–Munsell 100 hue test]] is very sensitive, but the [[Farnsworth–Munsell 100 hue test#D15 test|Farnsworth D-15]] is a simplified version used specifically for screening for CVD. In either case, the subject is asked to arrange a set of colored caps or chips to form a gradual transition of color between two anchor caps.<ref>((cite journal | vauthors = Kinnear PR, Sahraie A | title = New Farnsworth–Munsell 100 hue test norms of normal observers for each year of age 5–22 and for age decades 30–70 | journal = The British Journal of Ophthalmology | volume = 86 | issue = 12 | pages = 1408–11 | date = December 2002 | pmid = 12446376 | pmc = 1771429 | doi = 10.1136/bjo.86.12.1408 ))</ref>
* '''[[Anomaloscope]]s''' are typically designed to detect red–green deficiencies and are based on the [[anomaloscope#Principle|Rayleigh match]], which compares a mixture of red and green light in variable proportions to a fixed spectral yellow of variable luminosity. The subject must change the two variables until the colors appear to match. They are expensive and require expertise to administer, so they are generally only used in academic settings.

===Genetic testing===
While genetic testing cannot directly evaluate a subject's color vision ([[phenotype]]), most congenital color vision deficiencies are well-correlated with [[genotype]]. Therefore, the [[genotype]] can be directly evaluated and used to predict the [[phenotype]]. This is especially useful for [[Progressive disease|progressive]] forms that do not have a strongly color deficient phenotype at a young age. However, it can also be used to sequence the L- and M-Opsins on the X-chromosome, since the most common [[allele]]s of these two genes are known and have even been related to exact [[Spectral sensitivity|spectral sensitivities]] and peak wavelengths. A subject's color vision can therefore be classified through [[genetic testing]],<ref name=GHR2019>((Cite web|url=https://ghr.nlm.nih.gov/condition/color-vision-deficiency|title=Color vision deficiency|last=Reference|first=Genetics Home|website=Genetics Home Reference|language=en|access-date=2019-05-06))</ref> but this is just a prediction of the phenotype, since color vision can be affected by countless non-genetic factors such as your [[Retinal mosaic|cone mosaic]].

==Management==
Despite much recent improvement in [[gene therapy for color blindness]], there is currently no FDA approved treatment for any form of CVD, and otherwise no cure for CVD currently exists. Management of the condition by using lenses to alleviate symptoms or smartphone apps to aid with daily tasks is possible.

===Lenses===
((main|Color blind glasses))

There are three kinds of lenses that an individual can wear that can increase their accuracy in some color related tasks (although none of these will "''fix''" color blindness or grant the wearer normal color vision):

* A red-tint contact lens worn over the non-dominant eye will leverage [[binocular disparity]] to improve discrimination of some colors. However, it can make other colors more difficult to distinguish. A 1981 review of various studies to evaluate the effect of the X-chrom (one brand) contact lens concluded that, while the lens may allow the wearer to achieve a better score on certain color vision tests, it did not correct color vision in the natural environment.<ref>((cite journal | vauthors = Siegel IM | title = The X-Chrom lens. On seeing red | journal = Survey of Ophthalmology | volume = 25 | issue = 5 | pages = 312–24 | year = 1981 | pmid = 6971497 | doi = 10.1016/S0039-6257(81)80001-X ))</ref> A case history using the X-Chrom lens for a rod monochromat is reported<ref>((cite journal | vauthors = Zeltzer HI | title = Use of modified X-Chrom for relief of light dazzlement and color blindness of a rod monochromat | journal = Journal of the American Optometric Association | volume = 50 | issue = 7 | pages = 813–8 | date = July 1979 | pmid = 315420 ))</ref> and an X-Chrom manual is online.<ref>[https://artoptical.com/lenses/special-lens-designs/x-chrom/ An X-Chrom manual] ((webarchive|url=https://web.archive.org/web/20150412155316/https://artoptical.com/lenses/special-lens-designs/x-chrom/ |date=2015-04-12 )). Artoptical.com. Retrieved on 2016-12-10.</ref>
* Tinted glasses (e.g. Pilestone/Colorlite glasses) apply a tint (e.g. magenta) to incoming light that can distort colors in a way that makes some color tasks easier to complete. These glasses can circumvent many [[color vision test]]s, though this is typically not allowed.<ref name=FAA>((cite journal |last1=Welsh |first1=Kenneth W |title=Aeromedical implications of the X-chrom lens for improving color vision deficiencies |journal=Aviation, Space, and Environmental Medicine |date=April 1978 |volume=50 |issue=3 |pages=249–255 |publisher=Federal Aviation Administration |location=Oklahoma City |pmid=313209 |url=https://pubmed.ncbi.nlm.nih.gov/313209/ |access-date=30 September 2022))</ref>
* Glasses with a [[notch filter]] (e.g. [[EnChroma]] glasses) filter a narrow band of light that excites both the L and M cones (yellow–green wavelengths).<ref>((cite web|last1=Zhou|first1=Li|title=A Scientist Accidentally Developed Sunglasses That Could Correct Color Blindness|url=http://www.smithsonianmag.com/innovation/scientist-accidentally-developed-sunglasses-that-could-correct-color-blindness-180954456/?no-ist|website=Smithsonian|access-date=6 January 2018|language=en))</ref> When combined with an additional stopband in the short wavelength (blue) region, these lenses ''may'' constitute a [[neutral-density filter]] (have no color tint). They improve on the other lens types by causing less distortion of colors and will essentially increase the saturation of some colors. They will only work on trichromats (anomalous or normal), and unlike the other types, do not have a significant effect on Dichromats. The glasses do not significantly increase one's ability on color blind tests.<ref>((cite journal |last1=Gómez-Robledo |first1=L. |last2=Valero |first2=E. M. |last3=Huertas |first3=R. |last4=Martínez-Domingo |first4=M. A. |last5=Hernández-Andrés |first5=J. |title=Do EnChroma glasses improve color vision for colorblind subjects? |journal=Optics Express |date=29 October 2018 |volume=26 |issue=22 |pages=28693–28703 |doi=10.1364/OE.26.028693|pmid=30470042 |bibcode=2018OExpr..2628693G |s2cid=53721875 |doi-access=free |hdl=10481/57698 |hdl-access=free ))</ref>

===Aids===
Many mobile and computer applications have been developed to aid color blind individuals in completing color tasks:

* Some applications (e.g. [[color picker]]s) can identify the name (or coordinates within a [[color space]]) of a color on screen or the color of an object by using the device's camera.
* Some applications will make images easier to interpret by the color blind by enhancing color contrast in natural images and/or information graphics. These methods are generally called ''daltonization'' algorithms.<ref>((cite journal |last1=Simon-Liedtke |first1=Joschua Thomas |last2=Farup |first2=Ivar |title=Evaluating color vision deficiency daltonization methods using a behavioral visual-search method |journal=Journal of Visual Communication and Image Representation |date=February 2016 |volume=35 |pages=236–247 |doi=10.1016/j.jvcir.2015.12.014|hdl=11250/2461824 |hdl-access=free ))</ref>
* Some applications can simulate color blindness by applying a filter to an image or screen that reduces the gamut of an image to that of a specific type of color blindness. While they do not directly help color blind people, they allow those with normal color vision to understand how the color blind see the world. Their use can help improve inclusive design by allowing designers to simulate their own images to ensure they are accessible to the color blind.<ref>((Cite web|url=http://www.colourblindawareness.org/colour-blindness/colour-blindness-experience-it/ |title=Colour Blindness: Experience it|website=Colour Blind Awareness|language=en-US|access-date=2019-12-11))</ref>

In 2003, a cybernetic device called [[eyeborg]] was developed to allow the wearer to hear sounds representing different colors.<ref>Alfredo M. Ronchi: ''Eculture: Cultural Content in the Digital Age.'' Springer (New York, 2009). p. 319 ((ISBN|978-3-540-75273-8))</ref> Achromatopsic artist [[Neil Harbisson]] was the first to use such a device in early 2004; the eyeborg allowed him to start painting in color by memorizing the sound corresponding to each color. In 2012, at a [[TED Conference]], Harbisson explained how he could now perceive colors outside the ability of human vision.<ref>[http://www.ted.com/talks/neil_harbisson_i_listen_to_color.html "I listen to color"] ((webarchive|url=https://web.archive.org/web/20120812034717/http://www.ted.com/talks/neil_harbisson_i_listen_to_color.html |date=2012-08-12 )), Neil Harbisson at TED Global, 27 June 2012.</ref>

==Epidemiology==
{| class="wikitable" style = "float: right; margin-left:15px; text-align:center"
|+ Rates of color blindness((clarify|date=March 2014))<!--study? year? test sample?-->((citation needed|date=February 2020))
|-
! !! Males !! Females
|-
| '''Dichromacy''' || 2.4% || 0.03%
|-
| Protanopia || 1.3% || 0.02%
|-
| Deuteranopia || 1.2% || 0.01%
|-
| Tritanopia || 0.008% || 0.008%
|-
| '''Anomalous trichromacy''' || 6.3% || 0.37%
|-
| Protanomaly || 1.3% || 0.02%
|-
| Deuteranomaly || 5.0% || 0.35%
|-
| Tritanomaly || 0.0001% || 0.0001%
|}
Color blindness affects a large number of individuals, with protans and deutans being the most common types.<ref name=pmid21774112/> In individuals with Northern European ancestry, as many as 8 percent of men and 0.4 percent of women experience congenital color deficiency.<ref>((cite journal |last1=Birch|first1=Jennifer |title=Subjects with colour vision deficiency in the community: what do primary care physicians need to know? |journal=Journal of the Optical Society of America A |volume=29 |issue=3 |year=2012 |page=313-320 |doi=10.1364/JOSAA.29.000313|pmid=22472762 ))</ref> <ref>((cite journal |last1=Chan |first1=Xin |last2=Goh |first2=Shi |last3=Tan |first3=Ngiap |title=Subjects with colour vision deficiency in the community: what do primary care physicians need to know? |journal=Asia Pacific Family Medicine |volume=13 |issue=1 |year=2014 |page=10 |doi=10.1186/s12930-014-0010-3 |doi-access=free ))</ref> Interestingly, even Dalton's very first paper already arrived upon this 8% number:<ref name="Dalton1" />

((Blockquote
|text=...it is remarkable that, out of 25 pupils I once had, to whom I explained this subject, 2 were found to agree with me...
|author=John Dalton
|source=''Extraordinary facts relating to the vision of colours: with observations'' (1798)
))

==History==
[[File:US Flag color blind.png|thumb|An 1895 illustration of normal vision and various kinds of color blindness.]]
During the 17th and 18th century, several philosophers hypothesized that not all individuals perceived colors in the same way:<ref>((cite book |last1=Lanthony |first1=Philippe |title=The History of Color Blindness |date=2018 |publisher=Wayenborgh Publishing |isbn=978-90-6299-903-3 |page=3 |url=https://books.google.com/books?id=4qJ8DwAAQBAJ&pg=PA14 |access-date=14 April 2022))</ref>
((blockquote
|text=...there is no reason to suppose a perfect resemblance in the disposition of the Optic Nerve in all Men, since there is an infinite variety in every thing in Nature, and chiefly in those that are Material, 'tis therefore very probable that all Men see not the same Colours in the same Objects.
|author=[[Nicolas Malebranche]]
|source=''The search after truth'' (1674)
<ref>((cite book |last1=Malebranche |first1=Nicolas |title=Malebranch's search after truth, or, A treatise of the nature of the humane mind and of its management for avoiding error in the sciences : vol I: done out of French from the last edition. |date=1712 |orig-date=1674 |page=88 |url=https://quod.lib.umich.edu/cgi/t/text/pageviewer-idx?cc=eebo2;c=eebo2;idno=a51655.0001.001;seq=121;vid=60613;page=root;view=text |access-date=14 April 2022 |language=en))</ref>
))

((blockquote
|text=In the power of conceiving ''colors'', too, there are striking differences among individuals: and, indeed, I am inclined to suspect, that, in the greater number of instances, the supposed defects of sight in this respect ought to be ascribed rather to a defect in the power of conception.
|author=[[Dugald Stewart]]
|source=''Elements of the philosophy of the human mind'' (1792)
<ref>((cite book |last1=Stewart |first1=Dugald |author1-link=Dugald Stewart |title=Elements of the philosophy of the human mind |date=1792 |page=80 |edition=1 |url=https://quod.lib.umich.edu/m/moa/AJE6414.0001.001/94 |access-date=14 April 2022))</ref>
))

[[Gordon Lynn Walls]] claims<ref name="Walls56">((cite journal |last1=Walls |first1=Gordon L. |title=The G. Palmer Story (Or, "What It's Like, Sometimes, To Be A Scientist") |journal=Journal of the History of Medicine and Allied Sciences |date=1956 |volume=11 |issue=1 |pages=66–96 |doi=10.1093/jhmas/XI.1.66 |jstor=24619193 |pmid=13295579 |url=https://www.jstor.org/stable/24619193 |issn=0022-5045))</ref> that the first well-circulated case study of color blindness was published in a 1777 letter from Joseph Huddart to [[Joseph Priestley]], which described "Harris the Shoemaker" and several of his brothers with what would later be described as protanopia. There appear to be no earlier surviving historical mentions of color blindness, despite its prevalence.<ref name="Walls56"/>

The phenomenon only came to be scientifically studied in 1794, when English chemist [[John Dalton]] gave the first account of color blindness in a paper to the [[Manchester Literary and Philosophical Society]], which was published in 1798 as ''Extraordinary Facts relating to the Vision of Colours: With Observations''.((sfn|Lanthony|2018|p=14))<ref name="Dalton1">((cite journal |last1=Dalton |first1=John |author1-link=John Dalton |title=Extraordinary Facts relating to the Vision of Colours: With Observations |journal=Manchester Literary and Philosophical Society |date=1798 |volume=5 |issue=1 |pages=28–45 |url=https://digital.sciencehistory.org/works/fb4949523 |series=Memoirs |location=England, Manchester))</ref> Genetic analysis of Dalton's preserved eyeball confirmed him as having deuteranopia in 1995, some 150 years after his death.<ref>((cite journal |last1=Hunt|first1=D. M. |last2=Dulai |first2=K. S. |last3=Bowmaker |first3=J. K. |last4=Mollon |first4=J. D. |date=February 17, 1995 |title=The chemistry of John Dalton's color blindness |journal=Science |volume=267 |issue=5200 |pages=984–988 |doi=10.1126/science.7863342|pmid=7863342 |bibcode=1995Sci...267..984H |s2cid=6764146 ))</ref>

Influenced by Dalton, German writer [[J. W. von Goethe]] studied color vision abnormalities in 1798 by asking two young subjects to match pairs of colors.((sfn|Lanthony|2018|pp=25–26))

In 1837, [[August Seebeck]] first discriminated between protans and deutans (then as class I + II).<ref>((cite journal |last1=Seebeck |first1=August |title=Über den bei mancher Personen vorkommenden Mangel an Farbensinn |journal=Annalen der Physik |date=1837 |page=42))</ref><ref name="Walls56"/> He was also the first to develop an objective test method, where subjects sorted colored sheets of paper, and was the first to describe a female colorblind subject.<ref>((cite journal |last1=Lee |first1=BB |title=The evolution of concepts of color vision. |journal=Neurociencias |date=1 July 2008 |volume=4 |issue=4 |pages=209–224 |pmid=21593994|pmc=3095437 ))</ref>

In 1875, the [[Lagerlunda rail accident|Lagerlunda train crash]] in Sweden brought color blindness to the forefront. Following the crash, Professor [[Alarik Frithiof Holmgren]], a physiologist, investigated and concluded that the color blindness of the engineer (who had died) had caused the crash. Professor Holmgren then created the first test for color vision using multicolored skeins of wool to detect color blindness and thereby exclude the color blind from jobs in the transportation industry [[#Signal lights|requiring color vision to interpret safety signals]].<ref name=VC86>((cite journal | vauthors = Vingrys AJ, Cole BL | title = Origins of colour vision standards within the transport industry | journal = Ophthalmic & Physiological Optics | volume = 6 | issue = 4 | pages = 369–75 | year = 1986 | pmid = 3306566 | doi = 10.1111/j.1475-1313.1986.tb01155.x | s2cid = 41486427 ))</ref> However, there is a claim that there is no firm evidence that color deficiency did cause the collision, or that it might have not been the sole cause.<ref name=lagerlunda>((cite journal | vauthors = Mollon JD, Cavonius LR | title = The Lagerlunda collision and the introduction of color vision testing | journal = Survey of Ophthalmology | volume = 57 | issue = 2 | pages = 178–94 | year = 2012 | pmid = 22301271 | doi = 10.1016/j.survophthal.2011.10.003 ))</ref>

In 1920, [[Frederick William Edridge-Green]] devised an alternative theory of color vision and color blindness based on Newton's classification of 7 fundamental colors ([[ROYGBIV]]). Edridge-Green classified color vision based on how many distinct colors a subject could see in the spectrum. Normal subjects were termed ''hexachromic'' as they could not discern Indigo. Subjects with superior color vision, who could discern indigo, were ''heptachromic''. The color blind were therefore ''dichromic'' (equivalent to dichromacy) or ''tri-'', ''tetra-'' or ''pentachromic'' (anomalous trichromacy).<ref>((cite journal |last1=McLaren |first1=K. |title=Newton's indigo |journal=Color Research & Application |date=1985 |volume=10 |issue=4 |pages=225–229 |doi=10.1002/col.5080100411))</ref><ref>((cite journal |last1=Edridge-Green |first1=F. W. |title=Trichromic Vision and Anomalous Trichromatism |journal=Proceedings of the Royal Society of London. Series B, Containing Papers of a Biological Character |date=1913 |volume=86 |issue=586 |pages=164–170 |doi=10.1098/rspb.1913.0010 |jstor=80517 |s2cid=129045064 |url=https://www.jstor.org/stable/80517 |issn=0950-1193))</ref>

==Rights==
In the United States, under federal anti-discrimination laws such as the [[Americans with Disabilities Act of 1990|Americans with Disabilities Act]], color vision deficiencies have not been found to constitute a disability that triggers protection from workplace discrimination.

A Brazilian court ruled that the color blind are protected by the Inter-American Convention on the Elimination of All Forms of Discrimination against Person with Disabilities.<ref>((cite web |url=http://pt.scribd.com/doc/65834303/Acordao-Direito-Educacao-Deficientes | title=Full text of the decision of the court – in Portuguese language | access-date=2012-03-09 | url-status=dead | archive-url=https://archive.today/20120714220139/http://pt.scribd.com/doc/65834303/Acordao-Direito-Educacao-Deficientes | archive-date=2012-07-14 ))</ref><ref>((cite web |url=http://www.planalto.gov.br/ccivil_03/decreto/2001/d3956.htm | title=Decree issued by president of a republic ratifying Legislative Decree No. 198, of june 13, which approved the Inter-American Convention AG/RES. 1608 – in Portuguese language | access-date=2012-03-09 | url-status=live | archive-url=https://web.archive.org/web/20120325074802/http://www.planalto.gov.br/ccivil_03/decreto/2001/D3956.htm | archive-date=2012-03-25 ))</ref><ref>((cite web |url=http://www.oas.org/juridico/english/ga-res99/eres1608.htm | title=Inter-American Convention on the Elimination of All Forms of Discrimination against Person with Disabilities. | access-date=2012-03-09 | url-status=live | archive-url=https://web.archive.org/web/20130416205804/http://www.oas.org/juridico/english/ga-res99/eres1608.htm | archive-date=2013-04-16 ))</ref> At trial, it was decided that the carriers of color blindness have a right of access to wider knowledge, or the full enjoyment of their human condition.((citation needed|date=September 2021))

===Occupations===
Color blindness may make it difficult or impossible for a person to engage in certain activities. Persons with color blindness may be legally or practically barred from occupations in which color perception is an essential part of the job (''e.g.,'' mixing paint colors), or in which color perception is important for safety (''e.g.,'' operating vehicles in response to color-coded signals). This occupational safety principle originates from the aftermath of the 1875 [[Lagerlunda rail accident|Lagerlunda train crash]], which [[Alarik Frithiof Holmgren]] blamed on the color blindness of the engineer and created the first occupational screening test ([[Holmgren's wool test]]) against the color blind.<ref name=VC86/>

((Blockquote
|text=...I consider that to [Holmgren] above all others do we owe the present and future control of color-blindness on land and sea, by which life and property are safer, and the risks of travelling less.
|author=Benjamin Joy Jeffries
|source=''Color-blindness: Its Danger & Its Detection'' (1879)
))

Color vision is important for occupations using telephone or computer networking cabling, as the individual wires inside the cables are color-coded using green, orange, brown, blue and white colors.<ref>((cite book|last=Meyers|first=Michael|title=All in One A+ Certification Exam Guide|edition=4th|year=2002|publisher=McGraw-Hill/Osborne|location=Berkeley, California|isbn=978-0-07-222274-6|url=https://archive.org/details/allinoneacertif000meye))((page needed|date=August 2015))</ref> Electronic wiring, transformers, resistors, and capacitors are color-coded as well, using black, brown, red, orange, yellow, green, blue, violet, gray, white, silver, and gold.<ref>((cite book|last=Grob|first=Bernard|title=Basic Electronics|year=2001|publisher=Glencoe/McGraw-Hill|location=Columbus, Ohio|isbn=978-0-02-802253-6))((page needed|date=August 2015))</ref>

Participation, officiating and viewing sporting events can be impacted by color blindness. Professional football players [[Thomas Delaney]] and [[Fábio Carvalho (footballer, born 2002)|Fabio Carvalho]] have discussed the difficulties when color clashes occur, and research undertaken by FIFA has shown that enjoyment and player progression can be hampered by issues distinguishing the difference between the pitch and training objects or field markings.<ref>((Cite web|url=https://www.tacbis.eu/news/football-players-shocked-when-experiencing-colour-blindness/|title=Football players shocked when experiencing Colour Blindness|website=Tacbis))</ref> [[Snooker]] [[World Snooker Championship|World Champions]] [[Mark Williams (snooker player)|Mark Williams]] and [[Peter Ebdon]] sometimes need to ask the referee for help distinguishing between the red and brown balls due to their color blindness. Both have played foul shots on notable occasions by ((cuegloss|pot|potting)) the wrong ball.<ref>((cite web |url=http://www.billiardindex.com/MarkWilliams.html |title=Billiard Index: Mark Williams MBE player profile |website=Billiard Index |access-date=15 November 2023 |url-status=dead |archive-url=https://web.archive.org/web/20080708183938/http://www.billiardindex.com/MarkWilliams.html |archive-date=8 July 2008))</ref><ref>((cite web |title=Hawkins on Top Down Under |url=https://wst.tv/hawkins-on-top-down-under/ |url-status=dead |publisher=[[World Snooker Tour]] |date=2012-07-15 |access-date=2023-11-15 |archive-date=2023-10-17 |archive-url=https://web.archive.org/web/20231017161334/https://wst.tv/hawkins-on-top-down-under/))</ref><ref>((cite web |date=13 October 2008 |title=Rueful Ebdon mistakes brown for red |url=http://news.bbc.co.uk/sport2/hi/other_sports/snooker/7668421.stm |url-status=live |archive-url=https://web.archive.org/web/20120504082800/http://news.bbc.co.uk/sport2/hi/other_sports/snooker/7668421.stm |archive-date=4 May 2012 |access-date=15 November 2023 |work=[[BBC Sport]]))</ref>

===Driving===
((See also|#Traffic lights))
Red–green color blindness can make it difficult to drive, primarily due to the inability to differentiate red–amber–green [[traffic lights]]. Protans are further disadvantaged due to the darkened perception of reds, which can make it more difficult to quickly recognize brake lights.<ref name="Cole1">((cite journal |last1=Cole |first1=Barry |title=Colour Blindness and Driving |journal=Clinical and Experimental Optometry |date=September 2016 |volume=99 |issue=5 |pages=484–487 |doi=10.1111/cxo.12396|pmid=27470192 |s2cid=26368283 |doi-access=free ))</ref> In response, some countries have refused to grant [[driver's license]]s to individuals with color blindness:
* In April 2003, Romania removed color blindness from its list of disqualifying conditions for learner driver's licenses.<ref>((cite web |title=ORDIN 87 03/02/2003 – Portal Legislativ |url=http://legislatie.just.ro/Public/DetaliiDocumentAfis/42195 |website=PORTAL LEGISLATIV |publisher=Ministerul Justiției |access-date=31 December 2021| language=ro))</ref><ref>((cite web |title=ORDIN 87 03/02/2003 – Portal Legislativ |url=http://legislatie.just.ro/Public/DetaliiDocumentAfis/43242 |website=PORTAL LEGISLATIV |publisher=Ministerul Justiției |access-date=31 December 2021| language=ro))</ref> It is now qualified as a condition that could potentially compromise driver safety, therefore a driver may have to be evaluated by an authorized ophthalmologist to determine if they can drive safely. As of May 2008, there is an ongoing campaign to remove the legal restrictions that prohibit color blind citizens from getting driver's licenses.<ref>((cite web |last1=Corlăţean |first1=Titus |title=Discrimination against Romanians with genetic chromatic deficiencies |url=https://www.europarl.europa.eu/doceo/document/E-6-2008-2581_EN.html |access-date=31 December 2021|language=en))</ref>
* In June 2020, India relaxed its ban on driver's licenses for the color blind to now only apply to those with strong CVD. While previously restricted, those who test as mild or moderate can now pass the medical requirements.<ref>((cite news |author=<!--not stated--> |title=Mild to medium colour blind people can now obtain driver's license |url=http://timesofindia.indiatimes.com/articleshow/76645290.cms |work=[[The Times of India]] |agency=Press Trust of India |date=2020-06-26 |access-date=2022-06-01))</ref>
* Australia instituted a tiered ban on the color blind from obtaining commercial driver's licenses in 1994. This included a ban for all [[protan]]s, and a stipulation that [[deutan]]s must pass the [[Farnsworth Lantern]]. The stipulation on deutans was revoked in 1997 citing a lack of available test facilities, and the ban on protans was revoked in 2003.<ref name="Cole1" />
* All color blind individuals are banned from obtaining a driver's license in China<ref>((cite web |last1=Lu |first1=Feiran |title=Some of us see the world in a different light |url=https://www.shine.cn/feature/lifestyle/2108274147/ |website=Shine |access-date=1 June 2022))</ref> and since 2016 in Russia (2012 for dichromats).<ref>((cite web |title=Do color blindmen a driver's license. Color blindmen allowed to drive cars |url=https://rozavetrovsibir.ru/en/dokumenty/will-colorblinders-be-given-a-drivers-license-daltonik-allowed-to-drive-cars/ |website=Rozavet |access-date=1 June 2022))</ref>

===Piloting aircraft===
((See also|#Signal lights))
Although many aspects of aviation depend on color coding, only a few of them are critical enough to be interfered with by some milder types of color blindness. Some examples include [[Aviation light signals|color-gun signaling]] of aircraft that have lost radio communication, color-coded [[Precision approach path indicator|glide-path indications]] on runways, and the like. Some jurisdictions restrict the issuance of pilot credentials to persons with color blindness for this reason. Restrictions may be partial, allowing color-blind persons to obtain certification but with restrictions, or total, in which case color-blind persons are not permitted to obtain piloting credentials at all.<ref>((cite web |url=https://www.aopa.org/news-and-media/all-news/2012/january/01/answers-for-pilots-color-vision | title= Answers for Pilots: Color vision| date= January 2012))</ref>

In the United States, the [[Federal Aviation Administration]] requires that pilots be tested for normal color vision as part of their medical clearance in order to obtain the required medical certificate, a prerequisite to obtaining a pilot's certification. If testing reveals color blindness, the applicant may be issued a license with restrictions, such as no night flying and no flying by color signals—such a restriction effectively prevents a pilot from holding certain flying occupations, such as that of an airline pilot, although commercial pilot certification is still possible, and there are a few flying occupations that do not require night flight and thus are still available to those with restrictions due to color blindness (e.g., agricultural aviation). The government allows several types of tests, including medical standard tests (''e.g.,'' the [[Ishihara test|Ishihara]], [[Israel Dvorine|Dvorine]], and others) and specialized tests oriented specifically to the needs of aviation. If an applicant fails the standard tests, they will receive a restriction on their medical certificate that states: "Not valid for night flying or by color signal control". They may apply to the FAA to take a specialized test, administered by the FAA. Typically, this test is the "color vision light gun test". For this test an FAA inspector will meet the pilot at an airport with an operating control tower. The color [[Aviation light signals|signal light gun]] will be shone at the pilot from the tower, and they must identify the color. If they pass they may be issued a waiver, which states that the color vision test is no longer required during medical examinations. They will then receive a new medical certificate with the restriction removed. This was once a Statement of Demonstrated Ability (SODA), but the SODA was dropped, and converted to a simple waiver (letter) early in the 2000s.<ref>((cite web |url=http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item52/amd/ | title=Aerospace Medical Dispositions – Color vision | access-date=2009-04-11 | url-status=live | archive-url=https://web.archive.org/web/20090512031034/https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item52/amd/ | archive-date=2009-05-12 ))</ref>

Research published in 2009 carried out by the [[City University of London]]'s Applied Vision Research Centre, sponsored by the UK's [[Civil Aviation Authority]] and the U.S. Federal Aviation Administration, has established a more accurate assessment of color deficiencies in pilot applicants' red/green and yellow–blue color range which could lead to a 35% reduction in the number of prospective pilots who fail to meet the minimum medical threshold.<ref>((cite web|url=http://www.flightglobal.com/articles/2009/05/29/327137/colour-blindness-research-could-clear-more-pilots-to-fly-uk.html|title=Colour-blindness research could clear more pilots to fly: UK CAA|last=Warburton|first=Simon|date=29 May 2009|work=Air transport|publisher=Reed Business Information|access-date=29 October 2009|url-status=live|archive-url=https://web.archive.org/web/20090602082019/http://www.flightglobal.com/articles/2009/05/29/327137/colour-blindness-research-could-clear-more-pilots-to-fly-uk.html|archive-date=2 June 2009))</ref>

==See also==
((Portal|Medicine))
* [[Color agnosia]] – Ability to see colors, but inability to recognize colors.
* [[Color anomia]] – Ability to see colors, but inability to name colors.
* [[List of people with color blindness]]
* [[Motion blindness]]
* [[Tetrachromacy]]

==References==
((reflist|25em))

==Further reading==
((refbegin))
* ((cite book |last1=Kaiser |first1=Peter K. |last2=Boynton |first2=Robert M. |title=Human color vision |publisher=Optical Society of America |location=Washington, DC |year=1996|isbn=978-1-55752-461-4 |oclc=472932250 ))
* ((cite book |last=McIntyre |first=Donald |title=Colour blindness: causes and effects |publisher=Dalton Publishing |location=Chester |year=2002 |isbn=978-0-9541886-0-3 |oclc=49204679 ))
* ((cite book |last1=Rubin |first1=Melvin L. |last2=Cassin |first2=Barbara |last3=Solomon |first3=Sheila |title=Dictionary of eye terminology |publisher=Triad Pub. Co |location=Gainesville, Fla |year=1984|isbn=978-0-937404-07-2 |oclc=10375427))
* ((cite book |last=Shevell |first=Steven K. |title=The science of color |publisher=Elsevier |location=Amsterdam |year=2003|isbn=978-0-444-51251-2 |oclc=52271315))
* ((cite book |last1=Hilbert |first1=David |last2=Byrne |first2=Alexander |title=Readings on color |publisher=MIT Press |location=Cambridge, Mass |year=1997|isbn=978-0-262-52231-1 |oclc=35762680))
* ((cite book |last1=Stiles |first1=W. S. |last2=Wyszecki |first2=Günter |title=Color science: concepts and methods, quantitative data and formulae |publisher=John Wiley & Sons |location=Chichester |year=2000 |isbn=978-0-471-39918-6 |oclc=799532137))
* ((cite book |last1=Kuchenbecker |first1=J. |last2=Broschmann |first2=D. |title=Plates for color vision testing |publisher=Thieme |location=New York |year=2014 |isbn=978-3-13-175481-3))
* ((cite journal | vauthors = Dalton J | year = 1798 | title = Extraordinary facts relating to the vision of colours: with observations | journal = Memoirs of the Literary and Philosophical Society of Manchester | volume = 5 | pages = 28–45 | oclc=9879327))
((refend))

==External links==
((Commons category|Color blindness))
((Wikisource|Popular Science Monthly/Volume 19/May 1881/Color-Blindness))
* ((Curlie|Health/Conditions_and_Diseases/Eye_Disorders/Color_Blindness/))
* [http://tigger.uic.edu/~hilbert/Glossary.html "A Glossary of Color Science."] ((Webarchive|url=https://web.archive.org/web/20151004164334/http://tigger.uic.edu/~hilbert/Glossary.html |date=4 October 2015 ))

((Medical resources
 | DiseasesDB = 2999
 | ICD11  = ((ICD11|9D44))
 | ICD10  = ((ICD10|H53.5))
 | ICD9   = ((ICD9|368.5))
 | ICDO   =
 | OMIM   =
 | MedlinePlus   = 001002
 | eMedicineSubj =
 | MeshID = D003117
))
((Color vision))
((Eye pathology))
((Color topics))
((Authority control))

[[Category:Agnosia]]
[[Category:Color vision]]
[[Category:Visual disturbances and blindness]]
[[Category:X-linked recessive disorders]]
[[Category:Wikipedia medicine articles ready to translate]]
[[Category:Wikipedia neurology articles ready to translate]]

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