How well do you see colour?
The most usual cause of colour blindness is a fault in the development of one or more sets of retinal cones that perceive color in light and transmit that information to the optic nerve.
This type of colour blindness is usually a sex-linked condition. The genes that produce photopigments are carried on the X chromosome; if some of these genes are missing or damaged, color blindness will be expressed in males with a higher probability than in females because males only have one X chromosome - 1 out of 255 women and 1 out of 12 men have some form of colour vision deficiency.
Test how well you see colour here.