It's just a key that shows the different post milestones on this site, and the colors that coincide with them.  Everyone starts off as Amethyst (which is purple)  and the more you post, the higher your gemstone level. For instance, once you hit 100 posts your level changes to Saphire (I only know this because mine just changed, and now my username is printed in blue) the highest you can be is Stardust (which to me, looks periwinkle).  You may have noticed that everyones username (except the moderators) in the threads are different colors, and the color coincides with their current gemstone (post) level which is located beneath thier username.  Your gemstone is ruby, which is why your username is typed in red, which I think you may have hit after 50 posts. The usernames of the moderators and the Global Salon Moderator are in black and the stars beneath their names are blue and not yellow like everyone else's.  I hope I explained this correctly and somewhat clearly.