A couple more notes:

1) The change of scan rates by the ratio 1000/1001 was still within the looser original tolerance for monochrome. Changing the audio carrier frequency offset from 4.500 Mhz to (4.500)(1001/1000) would have been outside the original audio tolerance.

2) By the time that analog cable began messing up the burst on/off issue, all sources, color or monochrome, were running at color scan rates.

"and even the implemention of single-frequency networks where multiple transmitters cooperate to cover a given service area." - ATSC 3.0 ?

Yes, ATSC 3.0, but also possible in a few situations with ATSC 1.0, though much more limited in application and difficult to design.

Were there other color-under formats except for umatic, betamax, vhs and 8-mm? Like, the early Philips, or Grundig or some others? For example, the wikipedia article about the Philips format does not specify how the signal was recorded.

As far as I know, all domestic and industrial analogue videotape formats used colour under. That includes unusual machines like the Sony CV5600 (colour version of CV2100).

Possible exceptions are the IVC and Ampex 1" industrial formats that predate C format. In some case these had enough bandwidth to record colour directly. A special timebase corrector was needed to recover the colour. In the 1970s I had access to an unusual VR7003H (for high band) variant of the Ampex 1" machines. This certainly had the bandwidth but I never had a suitable TBC. You got flashes of colour on playback but certainly not useable.