The inner layer of the eye is composed of the retina, which receives the light focused by the cornea and lens. It detects the presence of light and its color, and sends this information to the brain for processing. The retina is lined with cells called photoreceptors. There are two kinds of photoreceptors: rods and cones. Rods detect the amount of light, whereas cones are stimulated by specific colors. If you had no cone cells, then you would be color-blind and would only be able to tell the amount of light present and not its color. When light hits the retina, different cells are stimulated in different locations. This map of stimulation corresponds to the world outside and is transmitted to the brain for processing and eventually turns into what we see.

Cross Section of Eye