Color

Color is the observation of light as it is reflected or absorbed by the human eye and processed by the brain. The actual distinction of colors occurs within the inner layer of the eye, the retina.

Inside the retina, four different kinds of light-sensitive receptors exist. The first are rods, which are responsible for general light absorption. The next three types are cones that absorb varied wavelengths. The length of the waves determines what kind of color is absorbed. Long wavelength absorbtion produces red colors; middle wavelengths produce greens; short wavelengths produce blues.

The capability for these cone receptors to absorb different wavelengths exists because of the pigments within them: a transmembrane protein called opsin which binds to the prosthetic group retinal, a type of Vitamin A. Rods employ a different kind of pigment called Rhodopsin, which is in the membrane of the outer section.

Rods are extremely sensitive to light. A single photon is enough to send signals to the brain.

The Spectrum

There are primarly seven groups of wavelengths that when interpreted in different ways are capable of producing the billions of observable colors that we see. Those groups are represented by a familiar mnemonic device: Roy G Biv, which stands for Red, Orange, Yellow, Green, Blue, Indigo, Violet.