Okay, I tried the second oscillator and the effect of the color adjust capacitor is definitely frequency. Based on the beat patterns it looks like the range of the capacitor is maybe 300ppm or so and (with very careful adjustment) it's possible to get the beat frequency down to a few ppm. SMPTE 170M specifies a tolerance of about 3ppm, but frequency differences of less than 30ppm or so are unlikely to be noticeable even with a TV which doesn't use the received color burst frequency.