On the blue-green flag above: I have no problem with the colors (NB: I am partially color-blind, but this shouldn't matter in this case), but what's that boomerang-looking thing? There are actually a few flags, or proposed flags, around that have this--I know I saw some.
On the black flag above: God, no. It looks like an ugly Christmas sweater.
On the five-color ROC flag: The five stripes stand for the five races of China, living in stratified harmony. Plus it looks too much like the Buddhist flag, or the gay pride flag.
If you're going to bring back a historical Chinese flag, I'd go with the Qing-era yellow flag with a blue dragon. Or if that's a bit too imperial, maybe change it to a yellow dragon on a red background.