Red, Green, Blue.
The three colours of light which can be mixed to produce any other colour.
Coloured images are often stored as a sequence of RGB triplets or as separate red, green and blue overlays though this is not the only possible representation (see CMYK
These colours correspond to the three "guns" in a colour cathode ray tube
and to the colour receptors in the human eye.
Often used as a synonym for colour, as in "RGB monitor" as opposed to monochrome