Since it's not down to the wood, and I'll take for granted that it's not through the color, a good, general chip filler that will work with most finishes is clear nail polish, take off a back plate or control cover and put a drop on a painted area, let it set for about two days and then check it with a fingernail to see if it's hardened, if it has it should be safe to use, clean the nick with a wipe of alcohol or lighter fluid, prop up the guitar so you can put a drop of the nail polish right down into the nick, let it set until dry, ( a couple of days ) you might have to repeat the process a few times, you want to just fill the hole in without building up a bump , it'll be ok to leave it a little concave ....... that's cheap and easy and hopefully all you'll need..........