Re: 'unused bit of the video signal'
Specifically, NTSC used 3.579545 MHz as the color subcarrier frequency. PAL used 4.433618 MHz. SECAM used a different system altogether that had its own tradeoffs (instead of both channels at once, it goes one at a time, improving horizontal color resolution at the cost of vertical resolution).
None of the systems were perfect, which is why derivise backronyms were made up ("Never Twice the Same Color", "Picture Always Lousy", and "Sans Experience Contre les AMericans"/"System Essentially Contrary to American Method")
Biting the hand that feeds IT
