He has difficulty naming red and green, but no problem with the other colors. P.S. Thanks so much for this wonderful website. I learn a lot each time I visit, and it helps fill in the gaps between visits. These rods and cones, as they are commonly called, fire a storm of nerve impulses in response to the light, which then travel down the optic nerve to the visual centers of the brain. The cones are responsible for the wonder of color vision.
Red light stimulates the red cones, and simultaneously inhibits the surrounding green cones.
All the rainbow of colors we see are a combination of these three primary colors of light. Another species could use a different number or group of colors as primaries. In kindergarten, children learn that red, yellow, and blue are the primary colors. The primary colors of light are red, blue, and green. As you add light together you get more wavelengths of light, and if you mix them all together you can get white light.