A colour is a name for certain kinds of flags.

• On land, it usually refers to regimental colours, but the term is also used outside military situations - for example, Boys Brigade as well as the Royal Rangers, Scout and Girl Guide flags are known as colours.
• At sea, the term "flying the colours" refers to a warship sailing on the high seas and flying its national ensign, thereby making its presence (and therefore its nation's military influence) known to other naval powers.