A diagram showing the relationship between the hue and saturation (1) dimensions of colours, differences in hue being represented by different positions around the circumference of the circle in their natural spectrum order, with similar hues close together and complementary colours opposite one another, and saturation represented by the distance from the centre, white light being situated at the centre and saturation increasing radially towards the circumference, a special segment of which is occupied by the non-spectral colour purple linking spectral blue with spectral red and completing the circle. Achromatic (1) colour is not represented, and therefore neither is the lightness dimension of colour. US color circle. See also metamer. Compare colour solid, colour triangle.