Colour vision deficiencies (CVD) (sometimes called colour blindness) represent a group of conditions that affect the perception of colour. Red-green colour vision defects are the most common form of colour vision deficiency.

CVDs are almost always inherited in an X-linked recessive pattern, although they can be acquired as a result of particular diseases and injuries. Males are affected by X-linked recessive disorders much more frequently than females since males have only one X chromosome and females have two, both X chromosomes on a female would have to have a genetic change in order to cause the disorder.

Males inherit their X chromosome from their mother and their Y chromosome from their father. Therefore, if a mother is a carrier of a CVD on one of her two X chromosomes, her son has a 50/50 chance of inheriting a CVD. Since females have two X chromosomes, one from the mother and one from the father they have less of a chance of being affected. About 8% (1 in 12) of males and 0.5% (1 in 200) of females have CVDs.

CVDs affect the ability to discriminate between certain colours such as red and green. A person with a CVD will try to discriminate colour differences by using other cues such as brightness differences. CVDs often do not impair quality of life but can affect career choices where colour discrimination is important for safety reasons.