Oh, okay.
It has just been my own personal experience that fake stones need to be piped as a child of a surface layer to avoid taking the surface of the terrain. If stones are added as displacement, they take on the color/texture of that layer. There could be a way to avoid that, not sure.
You must keep in mind when making your scene that when you assign altitude and slope to surface layers, if you want stones there make your stones a child of that layer.
Think how when you add a new surface layer you should see a white blanket over everything, then as you restrict altitude and/or slope you should see white triangles in your preview window where your restrictions are. When you add the stones as a child, uncheck the color option for the surface layer. Examine all tabs in layer controls. making sure something else is not interfering with your stones. (Like displacement at 100 or something, ha!)
This does not mean you cannot mask a layer, I was giving you a simple explanation.