ABSTRACT
A unique hue (also called an elemental or a pure hue) is one that is experienced as not being a mixture of other hues. For trichromatic humans, there are four unique hues—unmixed shades of blue, yellow, red, and green. The unique hues are colour classes: for instance, unique red includes all of the reddish greys, browns, and pinks that do not contain any blue or yellow. Philosophers sometimes write as if the unique hues were elementary colours. They are not always clear that to capture a single colour, they need to mention the absence of black and white. Colour experience is surprisingly complex, and there are many ways of systematizing and representing how it varies. Some representations privilege the unique hues as basic dimensions of chromatic experience. This entry reviews some of the key issues that arise out of these representations and the alternatives.
