Here are three pictures : normal, with one effect (shaded), with two effects (shaded and shaded 2 to give some relief) !
See the differences and the power of Moho...
A shape can have two effects. Simply have both effects being "Shaded" and you will have two shades.
(Actually, there is a way you can have an unlimited amount of shades. If you have the shaded object as a seperate layer you can use layer shading, and then put that layer in a group layer and give that group layer another layer shading, and then put that group layer in even another grouplayer and give that layer even another layer shading. I've used this method some times for 3D objects, to make them look better)