Ok time for another update - probably not quite as exciting as the last one. I went ahead and got some of of the buff cement colorant and was able to blend a much nicer brown color. After adding a little extra brown shading to the roots I'm much happier with how they look (I think the originally color was actually more purple than it appeared in my photos).
I've also covered the walls of the emersed portion with Ecoweb. The Ecoweb is really rough and cutting it up was a bit of a pain but I think it worked out pretty well in the end - here's how it looks:
I thought this stuff was supposed to be black but it's actually brown (quite similar to the color of my roots). It means there's a little less contrast with the roots but it does look more natural. Hopefully it will all be covered in moss/plants anyway so it shouldn't matter. Once I've got the water circulation system running I'm also going to incorporate a little bit of clay/peat/moss mixture into some parts of the background to hide the Ecoweb seams and provide a little bit of organic planting medium.
You may notice that I've also added in my drip lines at the top of the tank. As I had planned earlier, I used two lengths of 3/4" PVC (one for the back and one for the side) with holes drilled every inch or so. This should hopefully provide a nice even flow of water down the Ecoweb. I painted the PVC with two coats of black tinted Drylok so it wouldn't stand out so much.
I've also done a bunch of work with the plumbing/filtration system but I'm not going to post photo updates of that because it's probably not particularly interesting to most of the people on this board.
Well, this thing is pretty much ready to be water-tested. I'm just waiting for a few strong friends to come over to help me heave this behemoth onto the stand. I'm pretty confident with my construction so far, so I'm taking a gamble and moving this thing into its final location for the first fill. Hopefully the next update will be report good news rather than disaster!