Yes, I did remove the color boost circuits in the 1200XL. The way they do it, you can just crank up your COLOR control for the same effect.
The big problem in the 1200XL is the poor ground returns. This leaks CHROMA into the LUMA circuits and digital noise into everything. You cannot just drive video current into the outputs without getting ground noise.
You get transition colors because the video level changes the LUMA at the beginning of a clock cycle before the CHROMA phase has been decoded. The later the phase change, the worse the transition error. You could fix this by storing the RGBY decoded values in the monitor until the next cycle, but most (all, that I know of...) just run the LUMA thru a short delay line. This is why the DVD component video looks so good, the CHROMA is already decoded.