To form a color with RGB, three light beams (one red, one green, and one blue) must be superimposed (for example by emission from a black screen or by reflection from a white screen). Each of the three beams is called a component of that color, and each of them can have an arbitrary intensity, from fully off to fully on, in the mixture. The RGB color model is additive in the sense that if light beams of differing color (frequency) are superposed in space their light spectra adds up, wavelength for wavelength, to make up a resulting, total spectrum.This is in contrast to the subtractive color model, particularly the CMY Color Model, which applies to paints, inks, dyes and other substances whose color depends on reflecting certain components (frequencies) of the light under which we see them.
