Colour blindness results from an absence of colour-sensitive pigment in the cone cells of the retina, the nerve layer at the back of the eye that converts light into nerve signals that are sent to the brain. A person with colour blindness has trouble seeing red, green, blue, or mixtures of these colours.

Most colour vision problems are inherited and are present at birth. Other colour vision problems, called acquired coloured vision problems, are caused by aging, disease, injury to the eye, optic nerve problems, or a side effect of medicines. Inherited colour blindness is more common than acquired colour blindness and affects males far more often than females.

Inherited colour vision problems can't be treated or corrected. Some acquired colour vision problems can be treated, depending on the cause.