There is a flourishing field of colour science, one that goes back to Newton and includes such famous figures as Young, Maxwell, Helmholtz, and Hering. Almost all of this field has to do with the perception of colour, that is, to studying the conditions that cause or contribute to colours being seen, or to ways in which the colours as they appear may be studied. An example of the second kind of research is the many studies in colourimetry, involving the specification of colours. Typically these involve matching techniques in which the subject is asked to match some stimulus with one or another of a range of standardised cases.

One of the most vigorous areas of research, especially more recently, is the study of colour vision, i.e., of the mechanisms involved in the perception of colour. Helmholtz and Hering were pioneers in the physiology of this area, but much has been done recently in research on the neural processes involved in colour perception. A crucial development has been the growth in opponent-process theory. [See Kaiser and Boynton (1996) for technical discussion. See Hardin (1988) and Thompson (1995) for philosophically-informed discussions.] Also of significance are the experiments by Land and his colleagues and the development of his retinex theory of colour vision. [See Land (1983) and also Hardin (1988) and Thompson (1995) for critical discussion.] Uncovering the mechanisms that underlie colour vision is an exciting current field of research. The major philosophical relevance of such research is that it promises to help explain why some of the appearances of colour have the character that they do, e.g., why there are no reddish-greens nor bluish-yellows. If it becomes clear that appearances have a certain character which no set of objective physical features have, and that character can be found to based on the physiological/neural processes, then the research may be crucial in establishing that colour is best thought of not as some objective feature of the world that colour vision detects, but rather as something constructed by one's colour vision.

Another area of colour science has to deal with the construction of colour systems, i.e., of ways of ordering the range of colours in a systematic fashion. Usually this is done by constructing three dimensional colour solids. It is interesting, however that there are different systems that have been constructed. For one thing different dimensions are used depending on the way in which colour appears. Colours as properties of surfaces, in general, have a different mode of appearance from colours as properties of volumes such as wine, and yet again from that for film colour or aperture colour. These different modes of appearance suit different dimensions of colour. For surfaces the dimensions (at least in some systems) are hue, chromaticness and whiteness/blackness; for aperture or film colours the dimensions are hue, saturation and brightness.

Yet another field in which the way colours appear is crucial is the field of colour psychology: the field in which colour-constancy, simultaneous contrast, the effects of various backgrounds on colour perceptions, and so on, are examined, and competing explanations debated.

Almost all of this research in colour science is devoted to the way colour appears, i.e., to the conditions under which one perceives colour or experiences it or to the character of the way colour appears. Almost none of it is concerned with the other colour `truths', that is, to what we might call `causal truths and principles'. This is not to say that those `truths' or principles are false or are invalid. Biology and chemistry and indeed physics all use colour concepts and claims in their theories (some of them) and explanations, but there has not developed what might be called a "science of colour", except for the study of the way colour appears, or one might say, of the way colours are represented, and of the causes and conditions conducive to the way they appear and are recognised. That there is a flourishing field of colour science but not a science of colour reflects the special place colour has in science.

There is an important difference between colour science, on the one hand, and the science of shapes, geometry, the science of heat and temperature, and the science of sound, on the other hand. In the case of shapes and heat/temperature, and sounds and weights, we have properties of physical objects which we can detect, naturally and unreflectingly, by the use of our senses. These properties, however, are different from colours. In the case of shape and heat and weight and sound, there has developed a science in which the principles of sound, weight, heat, and shape are studied. There is however no parallel science of colour. There are few colour principles to serve as the basis for a science of colour. Colour science is a large field, but it is built around the way that colours appear and to the conditions under which colours can be perceived, and the causes which lead to the perception of colours. If colours ceased to appear in the distinctive ways then colour science would disappear.

The field of colour science has developed through building up theories and colour facts which contribute to our understanding of the perception of colour, as well as to provide an objective specification of colour. With both aims, the scientific account has to take account of a range of colour facts that hold of the practices and behaviour of colour-perceivers. That is, before we discovered any detailed scientific knowledge about colour, we had - and still have - a considerable body of knowledge about colour.

This body of colour knowledge is contained within the conceptual practices specific to colour. By studying these practices, we can draw up a set of general colour principles and `truths'. The range and extent of the general principles, have been emphasised by Justin Broackes (1992). [For further discussion, see Maund (1995).] These general facts or principles include causal truths, although the nature of the causal powers may be difficult to discern. It is easy to see that colour science has both filled out the details of some of the colour principles described previously, e.g., in respect to the internal relations and to the conditions under which colour is perceived, and in some case modified them. Furthermore, the discovery of colour-mixing laws and of the mechanisms underlying colour vision has added to our knowledge of colour.