Our trichromatic color vision is based on the responses of retinal photoreceptors belonging to three classes which differ in their sensitivities to light of different wavelengths. With this information from only three overlapping wavelength regions, we are able to see thousands of different colors. This makes color vision probably the most extreme example of hyperacuity .
Most mammals have no or only very limited color vision.
But the benefits of color vision are high enough that it has evolved in parallel in birds, fish, and even insects. Those species often rely not only on three, but on four, five, or more receptor types. Birds can additionaly have oil droplets as color filters in front of their photoreceptors. But even trichromatic color vision is not as simple as it might seem. Due to temporal and spatial interactions between colors , color appearance is not uniquely determined by the spectral distribution, as can be seen in the phenomena of induction and color constancy .