My big tank sat backgroundless for months and months because I couldn't decide. I finally bought the mirrored background and used the blue mirrored side, I liked it but I flipped it over to try the silverish side and I really liked it.
Seems to have cut down on the aggression that's been going on with my e. blue haps, they'd attack each other all the time and now that they're constantly seeing their reflection, they're a lot mellower.
I also have natural gravel mixed with crushed coral and my rocks have a lot of silver flecks, it all looks nice together.