Colors that are found in the visible spectrum are the colors of light. The three primary colors of light are theoretically red, green, and blue, although in practice they actually appear closer to red/orange, green, and blue/violet. Primary colors are the colors that cannot be created by mixing other colors, and theoretically from which all other colors are mixed. For the purpose of this program, I will refer to the primaries of light as red, green, and blue, or RGB. When these three primary colors of light are overlapped, the result is white light.

When two of these primary light colors are overlapped, the resulting light forms a new color, different from the original two and lighter than either of them. These resulting colors are known as secondary colors. Combining the correct proportion of red and green light produces yellow light, mixing green and blue light produces cyan, and a combination of red and blue light produces magenta.

This process of combining two colors of light to produce a new secondary color, or of combining all three light primaries to produce white light, is known as additive mixing.
Colors that are seen on a television screen, video display, or a computer monitor, or recorded by a scanner or film recorder, are the result of additive mixing of RGB color.

The three primary RGB colors are mixed using tiny dots or cells on the screen, and the resulting combination of dots makes up the image that is displayed. In a computer program, the user is typically offered a selection of colors to choose from, or is allowed to mix their own colors. When desiring color consistency across a majority of monitors, using colors in the 216-color Web Safe palette ensures colors will remain consistent on different monitors, even older ones. Some designers are beginning to use a larger palette of 4,096 colors called the Web Smart palette, which assumes that most users will view pages on recent model monitors.

Another way of looking at the secondary colors is to consider them the result of one of the primaries subtracted from white light. Cyan is white light with red light subtracted, magenta is white light with green light subtracted, and yellow is white light with blue light subtracted. These colors, cyan, magenta, and yellow (CMY) are used in what is known as the subtractive mixing process, discussed on the next page.