The eye has many parts within it's structure. The important parts that deal with light perception are the rods and cones, which are cells called photoreceptors that are in the retina of the eye.

Cones are the photoreceptors in the retina detect color and are activated when light intensity increase.

Rods are photoreceptors in the retina that allow us to see in dim light, but do not detect color.

The eye responds most strongly to red, green, and blue wavelengths, giving us our color vision.

http://www.stlukeseye.com/anatomy.htm