This may be the closest we'll get to The Dark Knight Trilogy in this game. This skin is the same as the player 1 default except it's more black than blue. It's noticeably different when playing Batman vs Batman.
All you have to do is; highlight Batman, press x(square for PS3)to bring up alternate costumes, then press start on Batman.
The outfit will look like this...


instead of this......


It looks better than my pictures show ;)
If this has been posted before, I apologize. For those of you who don't know about this, enjoy :)