There are three main types of partial colour blindness: Red deficiency (protanopia), green deficiency (deuteranopia) and blue deficiency (tritanopia).

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Photo by: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

The suffix -anopia refers to a complete absence of the cones that detect light, whereas -anomaly, as in deuteranomaly, tritanomaly and protanomaly, means the cones are present but mutated.

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Photo by: NASA/JPL-Caltech/University of Arizona

Roughly one percent of men have protanopia, and another one percent have deuteranopia. Deuteranomaly is the most common, affecting six percent of men and 0.4 percent of women.

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Photo by: Zeynel Cebeci

Tritanopia affects less than one percent of men and women, and tritanomaly affects less than 0.01 percent of men and women.

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Photo by: Wolfgang Roth

Most of the genes involved in colour blindness are on the X chromosome, which is why men are affected more than women.

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Photo by: Michael Maggs

Monochromacy is complete colour blindness. People with this condition see the world in black and white.

Want to check your colour perception? The EnChroma website has an easy Ishihara test.

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Photo by: Wassily Kandinsky, public domain

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