Their behaviors and appetites are a little different, at least re mine: the scarlets get bigger faster, and are more rock-pickers, while the blues are a shade more willing to persist on the sand-cleaning, and, being smaller, can get into places the scarlets won't quite fit---though a large scarlet has a bit of a reach. The scarlets are showier, and mine prefer coralline-encrusted shells---won't consider one that isn't: one has a two inch fighting-conch shell that's a bit big for him, but he hauls it about into the darndest places and seems to be the dominant one. The blues seem to like dark shells, and reject shells of equal size that aren't dark. They're great clowns, and have never harmed my corals.