Photochemistry of vision

Colors convey a lot of information to us from the surrounding world. Radiant sources (e.g. pixels on a monitor) combine the light into the resulting white, whereas by overlapping water lines on paper, we end up with black. Most people have three types of cones in their eyes that respond to different wavelengths of light. Why, however, does a spinning black-and-white disc appear colored to us? And what answers will students find to this provocative question? Let's try to start from the observation of the Benham disk, add other simpler experiments and show how much interesting (photo)chemistry we can observe and explain on the vision mechanism.