Usually I use separate layers for shading terrain and adding fake stones. You can....use the child but uncheck the color of that surface layer to keep the color you designate in your fake stone shader. You can also make an independent fake stone shader in shaders and hook a distribution shader to that.
When you are experimenting also check out effects....intersect underlying, favor rises or depression...neat stuff there too.
A very useful tool is the search tool too Martin, just give it the basics and usually get great results, although a personal reply is always great.