I presume you used the conventional methode, something like this. With smoothing enabled and no slope restrictions to the stones they should color any way you feed into the stones. Sometimes, especially in other methods where no compute terrain is used, a tex from XYZ shader (added like this, though it's not necessary here) helps to give the stones better displacement and colors.
In fact, while writing this; it would be good to be able to restrict stones to a certain slope, but still have it colored all over, which is not the case right now. If you set a max slope, the colors will be limited to that max slope too, which is no good.