Testors model paint works really well because its an enamel, just scuff the area with some fine sandpaper and put a dab on there. Its really durable on firearms as well. Comes in small bottles or you can also get it in paint markers. Just look at a hobby shop or somewhere like Michael's or JoAnn's. Its about the best stuff I have found for firearms because it is durable and the colors are bright and vibrant.