I've used nail polish (that's my usual choice, because it's easy) and auto touchup paint (not much luck matching the colors of my two bikes). Another possibility is Testor's model paint--a good hobby store may stock a few dozen colors, but you can get ANYTHING online, and it's cheap. My Atlantis is exactly the color Testor's calls "interior blue-green," to match the interiors of Russian military vehicles. Sorry I can't remember the website, but they have hundreds of colors. Try googling Testors, for a start.