Isn't that what the symbols behind peoples names are for? Recognizing who is ES (*), who is SMod/Admin (~), who is MSquid ($), and who is trial ES (%).
But I would agree it would be a very nice addition, even though some are already like that, include ES being purple, admins being red, legends being gold. It would make much more sense and cause less confusion.
IMO, MS should be dark green, SMods dark blue, CMods black. Not sure about HS though.
Come to think of it, many staff hold multiple staff positions so that's something to consider which color they would be. Maybe they could choose which one their self, like they can do (I'm pretty sure) on the forum.