The Commodores and the Ataris had a split video output. There are separate chrominance and luminance signals that get combined in the monitor. Or, an RF modulator output could feed a color TV on channel 2 or 3. The RF modulator output wasn't nearly as good. I used the Commodore 1902 monitors with the split video inputs, and I have used black and white closed circuit TV monitors with both the Commodore and Atari computers. I can't remember now if they had a composite video output, but they must have if I was able to use the CCTV monitors. It's been too many years since I looked at that stuff.
Anyway, if a person didn't have the proper type of Commodore split video monitor they would have to use the RF modulator output and a color TV set. The video quality would suck and would frustrate any one used to the sharp video quality of an IBM PC or similar computer.