Colors can be categorized as reddish or greenish, but rarely ever both. The same is true of yellow and blue. Now a new eye map shows how these hues are like oil and water in our brains. Subscribe to ...

Old World primates, including humans, have three types of cone photoreceptors that are maximally sensitive to long (L), middle (M) or short (S) wavelengths of light. In isolation, however, each cone ...