Some moral realists draw on the analogy between colours and values in order to claim that ‘desirability’ is a quality to which agents are sensitive under ideal conditions. The paper sets out objections to Michael Smith’s view that moral reasons are response-dependent and that they constitute the kind of reasons which would motivate ideal agents. The agent’s response to what appears to him or her morally desirable or morally mandatory is not a response in the same sense that our perception of a colour is a response to a disposition in the object to produce that perception. For a responsible agent appreciates values and reasons in the light of a plurality of moral considerations.