 One of the major problem, historically, concerns whether it is possible to reconcile the putative character of the intrinsic color features with such features having a causal role in our experiences of colors. The properties that do the causing of these experiences seem to be complex, micro-structural properties of surfaces of bodies (and similar properties for seeing volume colors, diffraction colors, scattering colors, etc). This problem is addressed by Hacker in his defense of the claim that colors are intrinsic features of physical bodies. He insists that colors are properties that are used to provide causal explanations. There is no more reason to deny this, he says, than there is to deny the parallel claim for solidity and liquidity. The explanation is not vitiated by the discovery that microstructural processes are involved, any more than explanations concerning solidity and liquidity are rendered otiose by the discovery of the microstructural base for these properties. A possible criticism of this analogy would be that, in the case of solidity and liquidity, it is plausible to analyze these properties functionally: to be solid is to have some structure that is the causal basis for such and such ways of behaving. This is not the sort of analysis that the Primitivist requires (see also Campbell 1994).