Hello Jeff,
You are correct that the CRT is monochrome and the LCD shutter at the front is enabling the color; however, there must be some display on CRT, for the time a specific color layer of the shutter is enabled, to show on the screen. In this case the whole display (monochrome CRT + shutter) is displaying correctly the CH4 blue trace (white on CRT and blue LCD layer ON), but the CRT, during the same period of time, is displaying something unintended, due to some defective (or un-powered) part.
I'll try to better understand the schematic (as of now I have a general idea how this works, but I don't know or understand all the details) and, in the meantime, I'll try to see if there isn't something that I missed at the right time, like a corroded trace in some hidden place or, plainly, a defective part.
Hopefully other people might have encountered something similar and might be available to provide some insight...
Thank you
TT
