I guess RO/DI has a strong affinity to strip out ions...
Black sand, black overflows .. seems a no-brainer to go black on the background.
I have that combo on a FW tank and it's really sharp. Only thing is in a reef, the rocks shed so much crud, you'll probably be doing a lot of vacuuming on your weekly chores. Hard to beat the look of a tank like that though!
