Match Hue not working

Hi,

I'm running FCP 7 in Mountain Lion and I've just noticed that the 'Match Hue' selection tool keeps giving me the same colour (usually black or grey) and will not allow me to balance colour between two shots. The selection tools for the Blacks, Mids, and Whites won't work either.

I recently installed Magic Bullet Suite, but after talking with their support it seems that's not the issue. I've trashed my FCP preferances but this didn't help.

I'm at a loss! Any help would be greatly appreciated!

Thanks,

Alan