This is for pure curiosity, can anyone explain? I'm wondering what the situation is in regard to the PAL colour subcarrier, which reportedly requires extreme accuracy... IIRC some of the TV stations have, or had, atomic standards for generating the CSC. In fact, as I understand it, the frequency of the subcarrier is calculated as some sort of multiple of frame and line frequencies, arranged so that the errors cancel from frame to frame. So what you'd really want is for the colour subcarrier to be locked to whatever frequency source generates your frame and line controls. Either the TV station transmits all 3, in that case the accuracy of the CSC is fairly irrelevant because everything is locked together at the source, or one or more of them is generated at the receiver end in which case the whole setup is governed by the quality of the oscillators in the receiver.
Or is the problem something to do with phase change during transmission?
Or is the whole question archaic because it's all going digital anyway?