EndlessFire has a good explanation with the threat squares, but it's not perfect. "If you're playing as white", while it is probably almost certain you are playing as white in a test area, technically you could be playing as black. So I put the two units in the game to compare and make a table:

I think it is obvious that the black RoyalGuard has a much more pronounced 'glow' effect in the middle of the shield. That is retained on the left unit here, but not on the right one. If you assume the colors were equally dropped on the right one, that one is White's.

-main_gi