Going off of what pinkrandomattack said, I'd go with painting gold on a blue background.
Except, it might be easier if you put down squares of paint tape (I'm thinking, like, the blue Scotch room tape. xD Not sure if that effects fabric though. I don't think so.) and then just paint over those and the fabric. Once all dry, you should be able to lift them up and have your perfect little squares of blue.
:]