Add a dry brush (a dry brush is a brush that has had most of the paint wiped of so it is 'dry; and then you apply the paint so it sticks to the raised surfaces only)
Add a wet / dry brush of green (by wet / dry I mean using the brush to pant over areas but not fill the deep cracks - so they remain black)
Add a wash of Devlan Mud - he's still shiney because I took the photo while the wash was still wet. (A wash is a much thinner type of paint, it will run into gaps and crevices and leave raised surfaces with a thinner coat making it great for shading)
Then I added red to the cloth areas (hat and loin cloth)
The red I gave a wash with devlan mud
Finally.. the finished product... well, I gave the green a very light drybrush to bring out the highlights such as the nose and the fingers up it.
Looks simple and fast, which is good for grots, and he has a grimy look at the end. The obvious thing to do once the unit/army is finished is to go back and work on the eyes, teeth, finger nails and hat fur. Which could be done pretty quickly and easily, even for a large group, and will really add to the model.
"True, true. These are rather dark times. How fortunate for me, then, that cats can see in the dark."