Adobe Acrobat 7 Professional - Manual (Page 682)

RGB model
A large percentage of the visible spectrum can be represented by mixing red, green, and
blue (RGB) colored light in various proportions and intensities. Where the colors overlap,
they create cyan, magenta, and yellow.
RGB colors are called additive colors because you create white by adding R, G, and B
together--that is, all light is reflected back to the eye. Additive colors are used for lighting,
television, and computer monitors. Your monitor, for example, creates color by emitting
light through red, green, and blue phosphors.
Additive color (RGB)