Honestly, if you have stopped doing whatever it was you were doing that made him upset, he should get over it. You can't control his mood and you're not responsible for it. As long as you're no longer doing whatever it was that was making him upset, and you've sincerely apologized for it, the best you can do is add to the positive things in his life. You know him better than any of us do; you know what he likes, what he wants from you, what he asks for. One of the things my little one does that always seems to discourage me from a sour mood is surprise me with something that I wasn't aware he knew about; he'll make dinner and say "We were out of your favorite brand of butter so I went out and bought some." and little thoughtful things like that usually make me adore him too much to be annoyed at anything, least of all him.

So maybe try doing that; just think about things your master likes, things he'll appreciate you doing; maybe things you don't usually do, as fetish suggested you can draw him a bath (if he likes baths), put his favorite music on, make his favorite dinner, get dressed up (or dressed down) for him when he comes home. Little things are everything, really.