Over time, the paint on the rims of a wheel has slowly been eaten by a set of brake pads.
- How do I strip left over paint?
- What type of paint should be used?
- How can I ensure the new paintjob will endure under friction from brake pads?
The braking surface on your rims shouldn't be painted, it will just reduce the brake's effectiveness and the paint will quickly wear out. In fact, over time rim brakes will actually wear down the metal on the braking surface. (After a lot of use, this area can get dangerously thin and the rims will need to be replaced.)
Painting below the braking surface is fine, although I don't have enough experience to give you any tips.
It's not paint that has worn off of your rims. It's anodizing. So it won't come off with a paint stripper.
Anodizing is an electro-chemical process often used to color aluminum bicycle parts. Some people actually do this at home. http://www.nonlintec.com/anodizing/ And there may be an electro-plating or anodizing shop in your locale who can re-anodize your bike rims.