I had this fault. The two likely issues are:Recapping the screen based on the advice on the other thread. To be honest. The screen is flickering more and more and happened 2 times to lose color and then coming back (neckbord probably) on it’s owm.
1) The soldering for the color drive transistors on the neck board. The transistors run really hot. The solder pads will most likely have come off. Reflow and apply jumper wires where necessary.
2) The pots on the neckboard for color cutoff and drive can get crusty. Fix it with spraying contact cleaner in them and then giving the pots some good full turns or swapping the pots for new ones.