I bought grey DryLock at Home Depot for my most recent terrarium project.
As posted above, it's easy to tint. You can pour a little into a large Mason jar to get the color right without risking the whole batch. It is a latex type paint, and I tinted mine darker for some areas using a very small amount of black latex trim paint.
Hindsight...I should have also blended in some brown and maybe a tiny bit of moss-green for a more natural color. I had intended to go over the whole thing with watered-down brownish-green acrylic paint afterwards, but couldn't find any locally and just went forward with grey.