The color extensions were added to the language in 1988 to provide more complete color functionality. With the original PostScript language, color could be specified using the red-green-blue (RGB) and hue-saturation-brightness (HSB) color models.
The color extensions include cyan-magenta-yellow-black (CMYK) color model, black generation and undercolor removal functions, screen and transfer functions for four separate color components, and a colorimage operator for rendering color sampled images. The color extensions are currently found in PostScript color printers from Canon, QMS, Oce, and NEC as well as all implementations of the Display PostScript system.