Trinitrons shifting white balance

[freakaftr8]

I probably already know the answer but just want to get your guys take on this.
I have a freebie KV40XBR800 and I had another one once as well and have noticed that they like to shift the white balance at times from white to a hint of green added. This seems to happen when the guns are predomantly showing all white then the screen changes to another scene that is darker. The g2 then carries back to pure white slowly. The g2 adjustment will help some to stop this but never fixes it. The g2 on these sets are really finicky. Only 1/8 turn in either direction will will either make the screen dark and muddy or shut down the set. Can't find a happy medium. Is this a weak CRT? I'd check it but can't.