" ... would be better served by showing that a black person CAN become a major power without resorting to disguise. Or am I missing something?"

Well - it sounds like you've come up with your own 'agenda' for the production. While being unfamiliar with the actual play in question, I think it is conceivable that a play that has to do with the relationship of the Crown to the issue of slavery might well require the Queen to be white to serve the vision of the playwright, if not just to make sense - unlike, I would suggest, the case of a play like Hamlet, which makes no reference to racial issues. But like Othello, which would surely lose something if a number of the actors playing leading roles were (obviously) Black - or if the actor playing Othello were obviously white (i.e., if his skin were not darkened with make-up).

By the way, Queen Elizabeth I apparently plastered herself in white make-up, so there is a precedent.

Another by the way: I recently saw a high school production of Macbeth, with a mixed-race cast - Duncan, the ill-fated king, was played by a black girl, with a tinfoil sword - and no 'white-face'. It's theatre, people! (Even in central Georgia ... It was interesting hearing Shakespeare with a southern drawl).