so far, IMO, Red sounds like the best choice. It easily represents the "Dawn" motif people have talked about, it represents the last third of a "Primary Color" trio with the first two films...it's a decent nod to "Batman: The Animated Series" (Obviously I would expect Nolan and Pfister to downplay it so that it's not 'blood-red skies' but still)...
And it feels to be the most fun and mosrt natural of the present choices.
Amber has been done in 'Begins.'
Blue has been done in 'TDK.'
Black/Gray is too bland.
Green is too 'Matrix.'
Orange is too bright.
Purple is too 'Joker.'
Yellow is too piss.
Brown is too poop.
Red is perfect.