Masking tape and foam don't mix. The foam underneath the tape isn't as strong as the paint... so the foam is what releases when you pull the tape... not the paint.

Your paint might well be water proof once it's set and dry... to the point it won't come off in water.

It sounds like what might be happening is you're trying to mask an area that you previously painted... and the color is coming off with the tape... because of the foam base it's on.

Have you actually tested a sample of dried paint with water... or is it that removing the masking tape is the problem? If it is the removal of the tape... just don't put tape on anything you've painted... rather use cardboard of something to create a "blind" when you paint. Sometimes some quite impressive graphics can be done with an airbrush and blinds for masking.

It's either that, or when you paint something on foam... plan the scheme so the masking tape only stays on unpainted areas. I hope this makes sense.

Michaels or Hobby Lobby will have alot of foam safe paint... and are great stores to get that stuff... yes most of which can be sprayed right out of the can. Watch out for weight using clears also... although a light coat is fine... you don't want to load it up with clear paint... and it actually won't help the paint stick to the foam any better.