The idea of admins was taken from Judge Dredd, but I can see how that wouldn't be obvious.
As for shirt colour, that was meant to be obvious. I realize the chromatic progression doesn't make much sense, but the point is to make them obviously different, and then to make the rank displayed with the combination of helm, gun, star, etc.
Saktoth: I was thinking about that, and I see your point. The icons of people aren't images that can be glanced at to make a clear connection to player skill, community status, or personal connection; at least not without having a reference document. A possible alternative would be to have letters in boxes to represent skill, both of which are coloured. Self/admin/friend could either have their username colour indicate this, or have a band of colour or text on the icon to signify it.