why don't you just use the same three colors as the logo and header? Blue - moderator, Green - Management, Yellow - Premium. Or if you don't want it to stand out as much just do grey/dark grey/black with white text.
...and maybe square off the corners to match everything else.
...I also wonder if premium really needs to have a "button" - maybe just one for moderator and management (not sure what that is). Mine for instance reads "premium member" then has "premium" underneath...kind of redundant and messy.