The color systems used by scientists and artists are entirely different. An artist will mix blue and yellow paint to get a shade of green; a scientist will mix green and red light to create yellow. The printed page in a magazine is yet another system.

Before you read any further, let's separate the two different kinds of color in the world. First, there's the color you can touch, such as the skin of an apple or a painted wall. These colors are part of the surface of an object. Next, there's the color you can't touch, such as a beam of red light and the colors produced by your computer monitor. Colors generated by light are part of one color system. The tangible colors which are on the surface of objects or on the printed page are another color system.

Scientists recognize the light primaries of red, green and blue. When combined, red and green light rays produce yellow, blue and green produce cyan, red and blue produce magenta. Red, green and blue mix to create white (light). Link to "How the eye sees color" for more information on the "additive" definition of light. This color model is used in computer monitors, television sets, and theater.

In subtractive color theory, all colors mix to yield black. In the print industry, cyan, magenta, yellow and black are used as the primary colors. When you mix all the colors, the result is gray.