I took a stab at painting the individual stones different shades of gray. I can't say that I am truly happy with the results. To my eye I allowed too much variation in the colors. Once it is fully dry I am going to hit it with some washes to see if I can tone it down and even-off the tonal variations. At least the thatch is almost right.
If you look at the photo of the real one you can see that the rocks are not al the same color, but mine has too much difference from rock to rock. I might have to re-think my painting program.