This behavior is also a cause of tetrachromacy in females: A mutation in a color receptor gene in one X chromosome only ends up affecting roughly half of the re

This behavior is also a cause of tetrachromacy in females: A mutation in a color receptor gene in one X chromosome only ends up affecting roughly half of the receptors of that type. The population of that receptor is then split between mutated and non-mutated, making the person sensitive to both the original wavelength (but less so) and a new wavelength, giving them four primaries and enhanced color separation - tetrachromacy. Even if the mutation is broken, they retain trichomacy - just with reduced light sensitivity. This is why women color blindness is rare, while men has no such backup.