Sometimes the picture is perfect but on some scenes,
about half a second to a second after the scene has
changed on screen, the colour suddenly either develops
a peachy-pink tone or appears to over-saturate. It
depends on what the picture on-screen is.

In what way?


This is also occurring with menus and on all video inputs.

That pretty much leaves out the color demodulator.

"Something" is wrong in (probably) the red amplification, or the red gun of
the CRT. You'll have to put a 'scope in the path and see what's fluctuating.