I've tried a couple paint designs that I found awesome looking for a themed case:
1. Ripped- for that cool "patina" look, all you need are a can of primer, and two other colors (one metallic preferrably), and a paper towel. Spray on 3 coats of primer, and two of the base color (non-metallic). Then, when dry, lightly spray over the base coat with the metallic color of your choice. Let dry, then spray one thin coat of base color over the metallic. Then, when the coat is dry, after a few weeks, you will notice the silver showing through. I thought this was neat when I used it in Project Trivium.
2. Textured- for those natural-looking silvers and golds, I made a textured design. I used Primer, metallic paint (I used silver), and an unused texturing item (please don't use things you will use later for other purposes lol). I sprayed on 3 coats of primer, and two coats of metallic color. I let that dry, then sprayed another layer of paint on. Then I used the object to create a textured design. Then I sealed the design with a couple more metallic coats and a couple clear coats.
Any questions, or comments?