I'll second removing normal alignment restrictions: only the Color Wheel really makes a lot of sense for those purposes. I'd also put forward that the Color Wheel alignment restrictions should probably be loosened. Just demand one of the two colors as the character's Primary, and leave it at that.

Ravnica was really the last block I played (and Invasion was the first ... fancy that), so I'll be keeping an eye on this. Let's see ... I ran Gruul, Simic, Orzhov and Dimir, so I'll be especially interested in seeing those.