Berlin and Kay (1969) present strong evidence that “all languages share a universal system of basic colour categorization” and that “the basic color-term inventories of most languages expand through time by lexicalizing these categories in a highly constrained, universal order” (Kay and McDaniel 1978:610). The validity of these conclusions has also been demonstrated by Collier et al. (1976) and by Kay and McDaniel (1978). The evolutionary process identified by Berlin and Kay can be represented schematically as follows:

where the arrow may be read ‘is encoded before’ (Kay and McDaniel 1978: 615). In other words, languages proceed through a series of stages in the development of their basic colour-term lexicon, with the most simplistic system containing only terms for white (light) and black (dark). Any expansion of this fundamental system will first result in the addition of a term for red and then in the addition of a term for green or yellow. If further expansion takes place, “yellow or green, whichever did not emerge at the previous stage, now emerges” (Berlin and Kay 1969:18), followed by terms for blue and brown. When a system develops beyond Stage VI, “there is a rapid expansion to the full roster of eleven basic color categories,” although no particular order of appearance among terms for purple, pink, orange, or gray has been ascertained (Berlin and Kay 1969:21-22).