One consequence of this setup that people might remember: the Nintendo Entertainment System can produce a "color" below the standard black level because of the primitive (albeit clever) scheme used to generate the video signal. It's been alleged that this was forbidden for licensed games, but a few games (and the Game Genie) did use it [1], causing an unstable image on some TVs.

[1] http://wiki.nesdev.com/w/index.php/Color_$0D_games