What is "tetrachromacy"

n. The quality of having four independent channels for conveying color information in the eye.

Tetrachromacy is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cells in the eye. Organisms with tetrachromacy are called tetrachromats.

In tetrachromatic organisms, the sensory color space is four-dimensional, meaning that to match the sensory effect of arbitrarily chosen spectra of light within their visible spectrum requires mixtures of at least four primary colors.

Tetrachromacy is demonstrated among several species of birds, fish, amphibians, reptiles, insects and some mammals. It was the normal condition of most mammals in the past; a genetic change made the majority of species of this class eventually lose two of their four cones.