Source : Free On-Line Dictionary of Computing

RGB
     
        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} and {HSV}).  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} (black and white).