Colour blindness
A reduced ability to tell certain colours apart, most often reds from greens.
Also: colour vision deficiency, CVD
Colour blindness is usually inherited and is far more common in men than in women, because the genes involved sit on the X chromosome. Figures often quoted are about one man in twelve and one woman in two hundred, though rates vary between populations. The usual form makes reds, greens, browns and oranges hard to tell apart. Blue-yellow confusion is rarer, and seeing no colour at all is very rare. Good design never relies on colour alone: a chart or signal should also use shape, position, pattern or text.