Sergio of the Kings is supposed to change your hair for you. But he's never given this option to me, and always refuses. i've completed all the quests for the King. He gives no new dialogue options anymore, just recites the same info about Freeside over an over.
You have to officially join the kings. Go back to the King you get one request for doing all of those missions, one option is to join them. If you chose something else you will never get a hair cut again.
Huh, I've never even heard of this guy. Then again I didn't really care for the Kings or the douchebaggery of quest that followed. But I remember hearing something about being able to change your appearance in Old World Blues, (The DLC that was released today), but I can't confirm this myself.