I'm trying to put together a list of people who have analogized morality to color in defense of one metaethical view or another. The best example I know about is John McDowell in "Values and Secondary Qualities." Geoffrey Sayre-McCord briefly uses the analogy in a defense of nonreductive realism in "Moral Theory And Explanatory Impotence." And in old times, there's Hume, who wrote, "Vice and virtue, therefore, may be compar'd to sounds, colours, heat and cold, which according to modern philosophy, are not qualities in objects, but perceptions in the mind."
Does anybody else spring to mind?