The abbreviation for the primary transparent ink colours needed to an acceptably full range of colours for something like a photograph. Stands for Cyan, Magenta, Yellow and Black. The letter K is used for black, partly because it avoids possible confusion with B for Blue. K actually stands for Key, dating back to when colours were printed in four separate passes (as is still often the case for screen printing). Black was printed first, then this image was used as a guide, or key, to register (align) all the other colours to. See: RGB, colour separation, process colour. See Spot Colour, Process Colour.