Color blindness most often involves difficulty telling red from green rather than seeing no color at all.

The longer version

The common forms trace to the genes for the long- and medium-wave cone pigments, which sit close together and are prone to copying errors. One variant may be missing or shifted, so red and green produce overlapping signals and the two hues become hard to separate.

Because the genes are on the X chromosome, the trait shows up far more often in males than in females. Total color blindness, with no working cones at all, is rare and brings poor daytime vision along with it. Many affected people learn to judge ripeness or wiring by brightness and position instead.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.