I've used the Quikrete over carved foam a couple of times and I tinted the different layers Quikrete with non-toxic acrylic craft paint, lightest as the first layer then darker as I went on. Before it was fully set, I ground away with sand paper to get a more realistic look. Here's some more details and pictures: http://www.frogforum.net/vivarium-terrarium-enclosure-discussion/6151-fire-bellied-toad-tank-under-construction.html

Here's a link to a thread on dendroboard which is probably the best example of cement rocks I've ever seen. I'm embarrassed to put my own efforts in the same thread http://www.dendroboard.com/forum/mem...struction.html Here the rocks were painted after the cement cured. From later pics in the thread it looks like it held up well (there was a problem with the tank thoguh) so I'm going to attempt this on my next viv.