I just received my new rev C 12″ PowerBook Sitting side by side with a Rev A machine I can tell you this:
1) Brightness: not much difference, about the same (after compensating for the fact that older machine has 1 year of use on it),
2) Color: much better. You can definitely see richer colors and more details.
[…] But in my opinion the 12″ screen on the Rev A was not as rich as my wife’s 700 MHz iBook. But this display (rev C) definitely is an improvement.