One of the standard models of describing colour space is shown in Figure I. This is the model shown in Kay & McDaniel (1978). The spherical model, with its four points of equal status along the equator (red, yellow, green, blue), is justified physiologically (De Valois et al. 1966). In Archibald (1989) I pointed out that the spherical model has great difficulty accounting for the distribution of basic colour terms on the colour solid. Similarly, the model cannot explain why terms at certain points on the model are basic while terms at other points are non-basic. Ultimately, we should like our model to be able to account for these lexical facts.