What is color blindness?

It is extremely rare that a person will have a total inability to see color. What is generally called color blindness might better be termed "color confusion." Most people with this disorder see colors, but tend to confuse some colors with others.

Color blindness, an inherited condition, is thought to be caused by either a lack of or a reduced number of cones of a given type. Which colors are affected and to what degree depend largely upon the type of cone involved. If all three types of cones are affected, the result is someone who sees the world like a black-and-white movie. But such a condition is rare.

Curiously, considering the universal traffic colors for stop and go, the most commonly confused colors are red and green.