Colors would not be possible without light because color is, in essence, light either reflected off of objects we see or viewed directly from the light source. When light is passed through a prism, the light beam bends and the wavelengths are separated, causing the prism to produce the colors of the electromagnetic spectrum. Rainbows are light bent through water particles in the air. Humans can only perceive a small portion of the electromagnetic spectrum - from 4.3-7.5 x 10¹⁴ Hz in frequency - and it is the frequency of the radiation that determines the color of light that we are seeing. Each color has its own wavelength. Infrared, microwave, radio, television and electrical power have lower frequencies than visible light, and ultraviolet, X-rays and gamma rays have higher frequencies.

Unlike the primary colors of pigment, the primary colors of light are red, green (not yellow) and blue, commonly referred to as RGB. The pigment color system does not apply to computer monitors because colors are created on monitors by adding light. RGB is an additive color system, which means that color is added to a black background. Black is the absence of light and therefore the absence of color. Secondary colors, such as cyan, magenta and yellow, are created by combining the primary colors. The color white is achieved by adding the three primary colors together in equal amounts.

There is, however, a third color system called subtractive, commonly referred to as CMYK. The primary colors of the subtractive system are cyan (C), magenta (M) and yellow (Y), the same colors that are the secondary colors of the RGB system. The letter "K" in CMYK stands for black. The subtractive color process is based on light reflected from an object and passed through pigments or dyes that absorb certain wavelengths, allowing others to be reflected. Unlike the additive system, which begins with black and adds color, the subtractive system begins with white and subtracts color. CMYK is commonly used in printing as most print begins with a white page that reflects white (RGB) light. To reproduce color on the paper, transparent pigments (cyan, magenta and yellow) are used to filter out the RGB wavelengths in various combinations. In theory, the combination of these three colors should produce black, but the fourth color black in CMYK is needed to produce true black. The secondary colors of the subtractive system are red, green and blue, the primary colors of the additive system.

The following links provide further information on the science of color.

RGB World
RGB Color Codes and Names Arranged by Hue
The Primary Colors Are Not Red, Yellow and Blue
Understanding Color
Secrets of Web Color Revealed
Application of Color for Digital Media