Primary Colors

Any set of three colors which when added in appropriate combination will yield white can be considered to be primary colors. It is useful to map color space with a set of primaries like blue, green, and red. If unit amounts of B,G, and R produce white light, then they can be used like unit vectors to define the color space. The coordinates of a point in space defines a color C by

The coordinates B, G, and R are called the tristimulus values with respect to that set of primaries. Early research was done with a specific set of RGB primaries. The same color can be quantitatively matched to the CIE primaries and expressed in terms of the CIE chromaticity coordinates.