Because I have coast to coast overflow with black acrilic backing I went with black garbage bags as I like if needed pull the bag off or aside to get a back view at times.
If I had to do it again I would have painted royal and light blue mix over the outline of my rock work and stay with black from that line down the entire back giving it the deep cave look from the rock down and the wavy ocean look over the rock line.
that said my vote is black.

I have to ask - are you the Eli we were chatting with in Concept today? Lol

Yes that's me.:biggrin:

Figured