I can't speak, at least in any manner that would be sufficient to askhistorians, about the question of cut off points, but I can at least provide some color to your second question (which isn't really a history question, but more a technology question). NTSC (the broadcast standard in the US) overlaid the color information (chrominance) on a second carrier wave in the TV signal. Audio and luminance didn't change (luminance being the brightness of the image at that point, chrominance being the color absent brightness). B&W TV is the luminance signal and the audio signal, which is why when color was added, B&W TVs could still receive the signal. They just never used the separate chrominance portion of the signal. So there's fundamentally no difference in the audio portion between B&W and Color. I suspect the differences you're talking about (and its subjective, so I'm not positive what you're hearing that led to the question) is actually just differences in the audio hardware (microphones, etc) over different periods of time. Although, its also worth noting that TV through the mid to late 50's predated magnetic recording, so early TV programs were often recorded basically with a film camera pointing at a CRT (a system known as Kinescope), and that process would degrade the sound and picture quality. (The history of that alone is interesting -- "live" TV was often time-shifted for the west-coast by filming it with Kinescope, quickly developing it, and then broadcasting the kinescope version three hours later!)

If that's the "voice" you're talking about, that's because what you're seeing in 2016 is not the same signal people would've seen with the original broadcast, its the kinescope copies, which don't have nearly the same fidelity. That's why you'll see substantial quality differences in both video and audio between recordings of things like the moon landings in the late 60's, versus news programs from the late 50's. People at home wouldn't have seen as substantial a difference.

From a comment I made a year ago to a similar question:

It is also worth noting that in 1964, only 3% of households that owned a television, had a color television. By 1968, color TV adoption rate had jumped to nearly 25%. By 1972, it was 52%. By 1990, it was 96%.

So at the time of the Zapruder film, only a tiny fraction of the population owned color televisions. It was difficult for the broadcast networks and affiliates to justify the expense of upgrading to new equipment. All the networks, but one that is.

At the time, NBC was owned by RCA, the prime driver for color television (and owner of most of the patents). So in November 1960 NBC started airing the bulk of its daily broadcasts in color, and by 1965 the vast majority of its primetime programming was in color.

ABC and especially CBS lagged far behind, airing only a handful of programs in color. In 1963, CBS would only air a program in color if the advertisers paid for the added expense. Consequently, they had only three color shows per week.

By 1965, color television reached the tipping point. Color TV sales started to surge, and by the end of that year nearly 10% of the viewing public had color televisions. ABC and CBS finally got on board and both announced they would go all-color for the 1966-1967 season.

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