Why on earth would anyone want to sit in front of a TV set and watch a screen with nothing but snow?
I can understand someone looking for distant signals doing this, but to simply stare at a blank screen with color snow (sounds like the color killer adjustment may have been a bit off as well, as the color will disappear from the snow when the killer is properly set), well, I have to wonder. What was going on? Even if the local stations weren't broadcasting color shows from the networks, etc. they would still have b&w shows on (old movies and the like).
I remember seeing color pictures in TV textbooks of the green stripe test signal, but I never actually saw it first-hand on any of the local TV stations in Cleveland.
BTW, in color TV's early years, some manufacturers put color indicator lights on the front panels of sets which would illuminate when the station to which the set was tuned was telecasting in color (technically, when the 3.579545-MHz--what all TV people today call "three-point-five-eight"--color-burst signal was being transmitted with the station's monochrome carrier). RCA used three such lamps to illuminate the color controls on the front panel when a color show was on, Motorola had its color indicator behind a rainbow-colored lens on some of its sets (IIRC), and so on.
I don't recall if Zenith used a color indicator on its early color sets, though I honestly don't think so. For example, the Zenith 29JC20 from the early '60s, IIRC, did not have a color indicator anywhere on the panel that I could see (I remember we had one of these sets in the electronics shop in high school, 30+ years ago, which is how I know what the table model 29JC20 looks like).