Sounds like a drifty voltage (or ground connection) that feeds your RED drive transitor, each time you press the button it 'normalises' the voltage (or ground) so the tranny drives a normal WHITE colour and reverts back to pink when you stop pressing the menu buttons.

Sounds like some kind of unregulation (filter cap) for the volts that goes to the driver trannies.

A quick fix might also be to remove the neck PCB off the rear of the tube, and re-fit it, those poins can be intermittent/corrosive due to the high voltages pumping thru them.
I fixed monitors for 25 years, and have seen a lot of weird faults, yet i'm sure there's 1,000's i havent seen yet hehehehe

Food for thought.
MM.