You’re right. It would cancel out in B-y r-y. Sorry. I ran into this long ago with a camera that during service got switched from yuv to rgb, then rgb was recorded into a betacam. We had to stip setup off of G to get the colour balance right through a rgb to yuv converter to do a dub. Great fun.
I know there are also MII (panasonic) specs for yuv that are different from Betacam if there is any chance your monitor could be set for those.