As for a color opinion, I too like the look of light blue for depth but am going with black for now because of the black overflow.
Maybe down the road when the box is covered in algae I'll try blue. Cheap enough to try :biggrin:
Word of warning with this idea though;
Don't splash water on the back glass unless you can reach back there to clean it! I ended up with streaks on the 125g and couldn't clean it. It stood out badly against the black.

none, black, black. the two blacks are all in one systems (biocube rsm)

you can also use car tinting. I'm going to be putting it on my DT soon so that you cannot see through the tank from the front, but from the back you will be able to see into the tank, although it will be tinted.

I lucked out because my fish room wall behind the tank is free of equipment so I can change backgrounds much like you change sheets on your bed. Best of all I have a view thru the back pane and can clean it with a magnet just like the front.

i sprayed mine black- never had blue but i like the black

I might give this a try on the sides and leave the back blue for now. This might work really well on an in-wall.