Change the color of the disk. Spin the spinner clockwise and counter-clockwise. Check all of the colors that you see. Cones are important for color vision and for seeing in bright light. There are three types of cones, each of which is most sensitive to a particular wavelength of light.
Rods are important for seeing in low light.
It is possible that the colors seen in spinning Benham disks are the result of changes that occur in the retina and other parts of the visual system. For example, the spinning disks may activate neighboring areas of the retina differently. In other words, the black and white areas of the disk stimulate different parts of the retina. This alternating response may cause some type of interaction within the nervous system that generates colors. Another theory is that different types of cones take a different times to respond and that they stay activated for different amounts of time.