Colour blindness, also known as colour vision deficiency, is the decreased ability to see colour or differences in colour. Colour blindness can make some educational activities difficult. Buying fruit, picking clothing, and reading traffic lights can also be more challenging. Problems, however, are generally minor and most people adapt. People with total colour blindness may also have decreased visual acuity.

The most common cause of colour blindness is due to a fault in the development of one or more of the three sets of colour sensing cones in the eye. Males are more likely to be colour blind than females as the genes responsible for the most common forms of colour blindness are on the X chromosome. As females have two X chromosomes, a defect in one is typically compensated for by the other, while males only have one X chromosome. Colour blindness can also result from physical or chemical damage to the eye, optic nerve, or parts of the brain. Red-green colour blindness is the most common form, followed by blue-yellow colour blindness and total colour blindness. Red-green colour blindness affects up to 8% of males and 0.5% of females of Northern European descent. The ability to see colour also decreases in old age. Being colour blind may make people ineligible for certain jobs in certain countries. This may include pilot, train driver, and armed forces. The effect of colour blindness on artistic ability; however, is controversial. The ability to draw appears to be unchanged and a number of famous artists are believed to have been color blind.