I'm going from pure speculation here, based on what I have looked up and seen around, and so on.
The IF alignment, sets up the general response curve of the “front end” of the TV, and the marker generator is a tool to help set that up. And when out of tune, color is prob the first thing lost, much like a FM tuner that's borked, mono works, but you just can't get MPX stereo to work, no matter how hard you try to turn the fine tuning knob...
But as I said, just an educated guess.
