Color blindness

Color blindness (color vision deficiency) is an x-linked recessive trait. It means it is a trait that sits upon the X chromosome. The girls are XX and boys are XY, and a recessive trait can only be shown on the person if TWO recessive traits are present in the genotype. Girls would have to receive this trait both from their father and their mother to be affected. Since boys are XY, they only need one color blindness trait to be affected. Hence there is a greater probability that they would inherit it from either their mother or father.
It is recessive in the sense that if you have 1 normal copy of the X chromosome and 1 affected X chromosome; you are still able to see normally. That's why few women are color-blind. But in men, there is only 1 copy of the X chromosome present so if it is affected, then he will be color blind.
Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.
There is no treatment for color blindness nor is it any significant disability. However, it can be very frustrating for individuals affected by it. Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray. While this sort of condition is possible, it is extremely rare. Being color blind does keep one from performing certain jobs and makes others difficult.