Firstly as the |dvi| file contains a request for a colour by name, the actual mix of primary colours used to obtain the requested colour can be tuned to the characteristics of a particular printer. In the |dvips| driver the meanings of the colour names are defined in the header file |color.pro|. Users are encouraged to produce different versions of this file for any printers they use. By this means the same dvi file should produce colours of similar appearance when printed on printers with different colour characteristics.
Secondly, apart from the so called `process colours' that are produced by mixing primary colours during the print process, one may want to use `spot' or `custom' colours. Here a particular colour name does not refer to a mix of primaries, but to a particular ink. The parts of the document using this colour will be printed separately using this named ink colour.