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"In the U.S. 7% of the male population – or about 10.5 million men – and 0.4% of the female population either cannot distinguish red from green, or see red and green differently. Color blindness affects a significant amount of the population, and it is even more prevalent in more isolated populations with a smaller gene pools. It is mostly a genetic condition, though it can be caused by eye, nerve, or brain damage, or due to exposure to certain chemicals."