What is considered the rarest form of color blindness?

The story behind the answer

Blue is correct because tritan color vision deficiencies (tritanopia/tritanomaly) are the rarest, affecting roughly 0.002–0.01% of people. They involve the S-cones that detect short (blue) wavelengths. In contrast, red–green deficiencies are far more common, especially in males, because the red and green opsin genes sit on the X chromosome.

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