nail polish sucks for color longevity. automotive touch up or model enamel paint is the answer, far better than nail polish. better range of useful colours for bikes, too.

if you do use nail polish, don't be too concerned about using acetone to clean up messes: it'll be OK if you're fast and careful. as long as the enamel underneath is well set, and hard, it won't be affected by rubbing lightly with acetone, unless you've rattle-canned your frame, or have some other cheap paint on there for some reason, when acetone will be a concern.