I actually like a black background a little bit better because of the contrast and I definitely enjoyed the black starboard we had on the bottom of the 90. If you are going with black silicone, I think an all black tank would look really sharp.
Those LED light things are nice, but as everyone has said, coralline really kind of ruins all of these effects (even if you clean the glass, overflows get covered). I'd be more likely to want an all rock wall so that you can't even see the back and can affix corals pretty much everywhere, but I kind of feel like the foam walls would be tough to implement for a whole tank (they try to float and would be immensely heavy to fit in if you build them out of tank).