Next we start to add colors. The best piece of advice I can give is to use pictures of the real thing. That will give ideas for any rock coloring that we will be convincing in your area.
I started with Beige mixed with white and a little burnt umber. Next I did a little dry brushing on the surfaces to pull out the highs in the rock work.
Keep layering different colors (don't worry if the colors are still wet - you want them to blend together in most cases). Try some mixing of different colors to get varied results. Don't be afraid of using just a little white as well to pull some details on the rocks too!!