I'm a big fan of plain black backgrounds myself, the only trouble with those small explorer tanks....at least mine anyway......is that they don't come with a light fixture and there isn't much of a top "wondow" for letting light in, even if you have one sitting up there...which I don't on mine.
I tried a black background on mine and all it did was make it very hard to see anything in there....lol. I think if you plants some tall java fern along the back....or some other taller plant there, it could do alot to help.
Keep monkeying around with it until you get what you like Tech...it's got lots of possibilities and potential !
The tank looks great. I'd also like to congratulate you on resisting the urge to toss an oscar in there... I've heard all too many horror stories, and dealt with way too many people at work that put huge fish in tiny tanks. Once the anacharis in the corners starts growing a bit, you can trim off the tops and plant those to get some more density to it... I think it'll look even better in the next few months. Well done.