This is available, along with the frame/line/pixel sync info, on a connector pad-out just above the CPU on all mk2/mk2a players.

Why does this sound so much easier than PCA's video out project that has been mentioned before? A lot of people are put off by the horror stories of the costs involved with that, but what you described actually sounds remotely feasable. 8 bits is certainly enough for usable color.

-Mike