He's a Knight -- a figure from history. Knights were white men (OK, maybe some scholar will turn up an exception or two).
Should UMass consider a Minutewoman? MSU or Vandy come up with a black Spartan or an Asian Commodore?
Of course, the selection of a student to wear the costume should be unbiased -- male or female, black or white, Hispanic or Asian, whatever -- just the best person for the job.
Don't get me wrong, I'm not blindly against change or full recognition of the University's growing diversity. You can knock me for it, but the change in the Alma Mater lyrics was OK with me. There was a reason for that -- why should a female student have to sing about becoming a "Man".
But for this, no reason.