Research overview: why cats struggle with red-green discrimination

Human red-green color vision depends on having two long-wavelength cone types with closely spaced sensitivities, a feature most mammals lack. This survey reviews evidence that cats, as dichromats, cannot make the red-green discriminations central to primate color vision because they possess only one longer-wavelength cone class. To a cat, many reds and greens likely appear as variations in brightness or as similar muted hues rather than as the vivid, distinct colors a person perceives. The overview connects this limit to the evolutionary loss of cone diversity in nocturnal ancestors of carnivores. It also notes the practical implication that color-coded cues relying on red-green contrast are poor signals for cats. Understanding the missing red-green dimension prevents overestimating feline color vision while still acknowledging the real blue-yellow discrimination cats retain.