the name escapes me now but I have this black substrate called eco zyme or something similiar which would be perfect for your setup. It comes in black or brick red and it is for plants and geophagus sifters. It is kinda of expensive but looks really good. Also has minerals for plants better than sand. Maybe someone will chime in with the correct name. great looking tank by the way!
I'll definitely be posting pictures once i get the darker gravel. Now that I look at the pics i see that they didn't come out too well so I want to take a few more.