First the surface has to be dry for the paint to stick. Then the paint has to dry. By this time the snail would be quite dead. Most likely the paint would peel off after being submerged for a period of time anyway. Don't know what damage, if any it would do to the shell.

Well, they're apple snails, so they can survive out of water for quite a long time. (In fact, I intend to bring them out later to see if they'd like some lettuce.) I've read about breeders identifying males with blue nail polish and females with pink nail polish. But the problem is that all of these people keep the apple snails by themselves as pets, not with fish.

I guess I'll give up on the idea. I wouldn't want to hurt my fishies over something so trivial.

A marine grade epoxy would be the best choice if you where going to do it. The epoxy paint becomes inert after it dries. Keep reasearching it, maybe look for a snail forum and see what breeders say. Post if you find anything out.

I had an apple snail crawl out of a tank and sit behind the stand for 3-4 days. I put him back in the tank and he was right as rain in a couple hours. I hear that they can survive for upto a week out of water.

Yeah, it's true. Apparently some of the places they live will dry up sometimes, so they have a lung, and their trap door keeps them from drying out. They lay their eggs above the surface, too, save for a few species.

As it turns out, mine are probably another type of snail that's often confused with apple snails, but I'm still not sure.

I have no new word on the painting. The lady at the pet store hadn't heard of it before, and she's not sure what any kind of paint would do to the shell. (Fish aren't really her forte. Perhaps the guy would have known more.)