It has to do with post count and member status.
1 star, Mortal - Member with <10 posts
1 star, Apprentice - Member with <100 posts
2 stars, Wizard - Member with 100+ posts
3 stars, Posty McPosterpants - Member with a ridiculous number of posts
4 stars (Yellow) - Bartender
4 stars (Green) - Local Moderator
4 stars (Red) - Person about to be invaded by the Canim
5 stars, White Council - Global Moderator (Mickey, Ashton, and Blaze)
6 stars - Administrator (Me = Gatekeeper, Fred = The Merlin)