Mary has new kinds of experiences when she leaves the black and white room. The change is akin to the difference between seeing black and white films and seeing films in colour. That much is common ground in the debate over the knowledge argument. This suggests that an ultimately satisfying reply to the argument on behalf of physicalism should base itself on a plausible view about the nature of the experiences she has for the first time on leaving the black and white room. It is, after all, the nature of these experiences that lies at the heart of the argument’s intuitive appeal. In this chapter, I offer an account of colour experiences and explain how it tells us physicalists what is wrong with the knowledge argument.