Color blindness

   Color blindness is an impairment in the ability to perceive colors. Many people have difficulty distinguishing between various shades of color, but a few people cannot see one or more colors at all. People who are totally color-blind see everything as black, white, and intermediate shades of gray. Most color-blind people, however, are blind only to red or green or both, which they see as shades of gray. Few people are color-blind to blue and even fewer to yellow.