Primary Colors

The human eye is sensitive to a narrow band of electromagnetic radiation that lies in the wavelength range between 400 and 700 nanometers, commonly known as the visible light spectrum. This small span of electromagnetic radiation is the sole source of color. All of the wavelengths present in visible light form colorless white light when they are combined, but can be refracted and dispersed into their individual colors by means of a prism.

The colors red, green, and blue are classically considered the primary colors because they are fundamental to human vision. All other colors of the visible light spectrum can be produced by properly adding different combinations of these three colors. Moreover, adding equal amounts of red, green, and blue light produces white light and, therefore, these colors are also often described as the primary additive colors.

Interactive Java Tutorial

Primary Additive Colors

Explore how the primary additive colors interact with one another to form new colors.

As illustrated by means of the overlapping color circles in Figure 1, if equal portions of green and blue light are added together, the resultant color is cyan. Similarly, equal portions of green and red light produce the color yellow, and equal portions of red and blue light yield the color magenta. The colors cyan, magenta, and yellow are commonly termed the complementary colors because each complements one of the primary colors, meaning that the two colors can combine to create white light. For instance, yellow (red plus green) is the complement of blue because when the two colors are added together white light is produced. In the same way cyan (green plus blue) is the complement of red, and magenta (red plus blue) is the complement of green light.

via Molecular Expressions: Science, Optics, and You: Light and Color – Primary Colors.