Colour blindness (colour vision deficiency) is a condition in which certain colours cannot be distinguished, and is most commonly due to an inherited condition. Red/Green colour blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another colour deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.
Depending on just which figures you believe, colour blindness seems to occur in about 8% - 12% of males of European origin and about one-half of 1% of females. Total colour blindness (seeing in only shades of gray) is extremely rare.
There is no treatment for colour blindness, nor is it usually the cause of any significant disability. However, it can be very frustrating for individuals affected by it. Those who are not colour blind seem to have the misconception that colour blindness means that a colour blind person sees only in black and white or shades of gray. While this sort of condition is possible, it is extremely rare. Being colour blind does keep one from performing certain jobs and makes others difficult.