One of the touch-up techniques I've used for guitars and bikes (not vintage, nitro-finished guitars) is to use fingernail polish (acrylic lacquer). My last touch-up was a Stratocaster that was painted Seafoam Green (not too far from Celeste). I just mixed a tiny bit of the green pastel color with white in a small paper cup until I got the right mixture. This is great for small touch-ups where you don't need a whole can of paint.