 The Primitivist Realist needs to have some view about how colors are related to the physical properties of material objects, e.g., spectral reflectances, that are necessary in order for us to have experiences of color. That is to say, it is vital that they have some theory on the matter. The standard view has come to be that colors are supervenient on these physical properties. On some accounts, the supervenience relations are nomological ones; on other accounts, they are metaphysical (rather than logical)—see Hacker 1987, Campbell 1994, Yablo 1995, McGinn 1996, Watkins 2005. Appeals to supervenience are fine as far as they go but, as often been pointed out, they mark the start of an explanation, rather than the end (see entry on  supervenience).  We need to specify which kind of supervenience is involved: nomological, logical or metaphysical (where and if the latter can be distinguished from the logical form). Secondly, we need to give some account of what it is that grounds the supervenience relation. Byrne and Hilbert, in a complex paper specifically on Primitivism (2007a), argue that appeals to both nomological and metaphysical supervenience face formidable objections.