I've tried this with several of my tanks, and still waiting for things to grow in before I make a decision.
That's an etched glass window film on the back with white poster board behind it. There is an LED light strip in between so I can do things like:
But it doesn't really show up when the main lights are on
I tried this with another tank:
And just kind of sloppily mashed the two colors together somewhere in the middle. The idea was also to backlight it but again it's not really very impressive with the daylights on. Otherwise it looks like this:
That's backlit with an Aqueon 8000K full sprectrum from a 10 gallon I had laying around, there is also some daylight from a cliplight on a breeder box on the back of the tank.
I have a few other tanks with black paint and you really can't go wrong, unless of course you're going for that 'blue sky in the distance' look.
Also, light colored backgrounds mean cleaning the back of the tank too, cause anything growing on that pane shows up REALLY well against a light background.