A little trick a friend of mine who runs an automotive bodyshop taught me was to make a little paintbrush out of masking tape. Roll it up into a cone and mix up a small amount of paint and hardener (not sure if you need to bother with the thinner, don't think that has anything to do with it curing correctly?) and dab it into the chip using the pointed end of your 'brush'.
As we're talking solid colours here you can then just polish it back flush afterwards - a lot less mess than using an airbrush or spray gun.