Are 'Scientific' Objects Coloured?

'In a world of "scientific" objects, objects characterizable by the vocabulary of physics alone, in a world governed by what we now believe to be the laws of nature, can anything be coloured?' I am here concerned to examine the claims of those physicalists who are disposed to give an affirmative answer to that question. In so doing, I shall restrict my attention to the physics of the present time, helping myself to the rather generous assumption that the vocabulary and laws of physiology need not, in the last analysis, outrun those of physics. The physics of the present day is assuredly not engraved in stone, but the parts of it which have to do with the sources of electromagnetic radiation and its interaction with animal tissue-the only parts which have any conceivable bearing on colour vision-are unlikely to see significant revision.1 What are colours? It seems clear that a proper understanding of colours must proceed from sensory acquaintance: the congenitally blind man cannot have an adequate conception of colour. But it is equally apparent that colours are more than simple, ineffable qualia. Hume's missing shade of blue rather effectively makes that point. Our concept of colour involves not only manifest colours, but a whole set of ordering relationships among them. Every colour is specifiable by three dimensions: hue, brightness and saturation.2 Colours of a given hue may be linearly ordered according to brightness, if saturation is held constant, and according to saturation if brightness is held constant. Holding both brightness and saturation constant, the hues may be ordered in a closed array, the end points of the spectral hues being connected through an array of non-spectral purples. These relationships among colours cannot, of course, be extracted from the bare presentation of a single colour sample any more than its i 800 angle sum can be extracted from the