You're doing fine, don't panic! Whatever program you're using though created 23 colors out of a piece that doesn't have them. Upgrade to something decent. Look at this edit:
Don't try to immitate it! Try to think why I did what I did!
Flat surfaces at a 90 degree against the lightsource (sun above) catch the most light! Any sloped surface gets less! Some surfaces cast shadows on surfaces below them! Crevices are darker as they don't catch light! EDGES get speculars because they are edges. a pockmark on the stone is dark, and the lip of the hole is lighter because it is an EDGE.
Try to think of objects in three dimensions and apply a lightsource in a definite way to the rendering. Try to think how the lights would slowly smoothly move about if you rotated the lightsource around the object.
