So, in a 6 player round-robin, where each one played one of the mono-colors twice (alternating going first), I would expect something like:
Black (8-2)
Red (7-3)
Purple (6-4)
White (5-5)
Blue (3-7)
Green (1-9)
(not specifying which color would beat which, just figuring Green would get one win somewhere, and black would pick up a couple of losses)