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Yep, that could be handy, however isn't that what the colours are for and would it not be confusing to have the same colours for flags and colour ratings, maybe a user option??
I would say that colored flags would lead to confusion with colored labels. The flags are different for each status (reject, pick, and unflagged), so I suggest just getting used to that scheme. Of course, if Adobe added an option, that would be fine too.