I never really understood how using paint filled BBs would help. Even with indoor paintball, everyone's covered in paint after a few rounds. If you complain that someone ignored a hit, they could always claim it was from a previous game or diving into a dropped paintball behind a bunker. Even adding a ref doesn't change much as he or she can't see everything at once.
My point is that cheaters will cheat no matter what. Maybe marking BBs would deter some from cheating. Maybe not. Either way, I'd rather not play with people who'll knowingly ignore a hit if they think they can get away with it.