Monochromacy or monochromatism is very rare. People with this condition see as shades of grey. However, monochromacy is an umbrella term: those with the deficiency may mix up colors, such as yellow and white, green and blue, or red and black. There are three forms of this extreme color blindness: rod monochromacy, blue-cone monochromacy, and cerebral achromatopsia.

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