It has been argued that there is room for both objectivist and psychological concepts of colour, even though those providing analyses built on these concepts commonly see them as competitors. Properly interpreted, these accounts do no have to be sen as rivals. This claim can receives further support from consideration of two very different objectivist accounts, one by Jackson and Pargetter (1987), the other by David Hilbert (1987). Their respective solutions to some of the problems facing objectivism illustrate how each provides an objectivist concept of colour that fits comfortably with a psychological concept, as well as with each other.

Jackson and Pargetter, who claim that each colour can be identified with a physical property, have the explicit aim of overcoming the problem of multiple realisations. They concede that there is no single physical feature that is the basis for each colour say, blue, but maintain that this does not matter. Blue is identified with a different physical property on different occasions, depending on what kind of physical object has it. This means relativising the concept of colour, to kinds of objects and circumstances. In principle there is no reason why there should not be a concept of physical colour, in the way described by Jackson and Pargetter. The issue though is that we need some way to unify the various properties so as to bring them under the umbrella of colour, and on the face of it, the psychological concept seems necessary.

The point is a general one. The objectivist who attempts to identify the objective essence for colour must relate that essence to the way colours appear. Given that the criteria used by competent colour perceivers to identify colours, depend on the appearances, it is necessary for the objectivist to spell out the nature of this relation. For the subjectivist the appearances constitute (part of) what the essence is. for the objectivist the appearance picks out the essence which is independent of the appearance.

In determining the right objectivist candidate, our aim is not simply to show how colour vision enables, say, the observer to distinguish objects with different spectral reflectance characteristics. Rather we need to explain why one reflectance profile deserves to be classified as blue, and likewise why other profiles are related to similar and differing colours. Consequently to identify one reflectance profile as that corresponding to unique green, we need to be able to specify standard conditions and normal observers. As Hardin has persuasively pointed out, this cannot be done except in a highly arbitrary way. Not only is there a minority of colour perceivers who are anomalous (only slightly, but appreciably so) with respect to normal observers, but there is a considerable statistical spread even within the group of normal observers. The reflectance profile for unique green will differ for different members of the "normal group". One can decide, of course, on a standard and fix one reflectance profile as green, but the procedure is highly arbitrary. As we have seen, there are few interesting causal powers associated with colours apart from the way objects affect perceivers. There is an alternative, however, and that is to tie colour to appearance and, in consequence, relativise colour to observers, with as much freedom or restriction, according to context, as is required. The most natural way to relativise colour is through a dispositional concept that ties colour to the way it appears to observers of the right kind. Jackson's concept of physical colour would need to be supplemented by the dispositional concept. The admissibility of such a concept would not mean that the dispositional concept ought to be eliminated.

A novel twist to the objectivist program has been provided by David Hilbert (1987), with his account known as `Anthropocentric Realism'. It provides a solution to the multiple realisations problem but one that still seems to supplement the psychological concept, and not to dispense with it. On this view, colours are identified with spectral reflectances, at least surface colours are. A distinction is drawn between this kind of colour and anthropocentric colour. Individual anthropocentric colours are associated with groups of spectral reflectances. Colour perception and colour language `give us anthropocentrically defined kinds of colours and not colours themselves'. [Hilbert (1987) p. 27.] Terms such as `red', `blue', `yellow', etc are associated with anthropocentric colours. To be red, for example, is to have a reflectance that falls within a particular class of reflectances. These classes, in general, are highly anthropocentric, sharing few interesting causal powers, and being of little consequence, apart from how they connect with the peculiarities that underlie human colour vision. The principle of grouping is that a given perceived colour is associated with `a triple of integrated reflectances'. This association is based on the fact that human colour vision depends on the use of `three types of broad band sensors', i.e., the three types of light-sensitive receptors [Hilbert (1987) p. 111]

Colours, on this view, are both objective and anthropocentric. This would help explain why there is a colour science and no science of colour. It can also be readily modified so as to handle that problem whose resolution seems to require the relativisation of colour to kinds of observers. Once the concept of anthropocentric colour is in place, it can be relativised, if necessary, to groups of observers.

It is Hilbert's claim that with this analysis, many of the `common-sense claims' about colour can be preserved, e.g., that orange is more similar to red than it is to blue. The point is that the triples of integrated reflectances can be taken as co-ordinates in a three-dimensional space, thus defining a colour space. Similar colours will be located at adjacent points in this space. It is claimed that the right interpretation of statements of colour similarity and dissimilarity is in terms of statements about relative location in colour space.

It is with this claim that scepticism will most naturally arise. On the face of it, there is a certain qualitative character to ostensively defined colour space, e.g as expressed in the Munsell or Swedish Natural colour systems, that is not captured by the triple-reflectance colour space. One measure of this fact is that changes along the dimensions of brightness and saturation have a different character from changes of hue from unique green to unique yellow to red to blue. Changes in Hilbert's colour space don't seem to be of the right kind _ which of course is not to deny that they may not contribute to a causal explanation for why the psychological colour spaces have the character that they do.

To conclude: the existence of the various problems facing the objectivist proposals do not demonstrate that the objectivist concepts are not viable. The solutions offered, however, cast doubt on the claim that objectivist concepts stand in no need of supplementary psychological concepts of colour.