Has the joey detached from the nipple, or does mom just have him hanging out of her pouch for grooming. It is possible for two joeys in pouch to be different ages (different stages of development) so the pink joey just may not be mature enough to be OOP.
If the joey is not detached, do not try to handle it, let mom tuck it back in her pouch to grow a bit longer until it is really ready to be OOP.