java - How can I change this isometric engine to make it so that you could distinguish between blocks that are on different planes?

I have been working on an isometric minecraft-esque game engine for a strategy game I plan on making. As you can see, it really needs some sort of shading. It is difficult to distinguish between separate elevations when the camera is facing away from the slope because everything is the same shade. So my question is: can I shade just a specific section of a sprite? All of those blocks are just sprites, so if I shaded the entire image, it would shade the whole block. I am using LWJGL. Are there any other approaches to take?

Here is a screenshot from the engine:

Answer

One possible solution would be drawing edges along where the terrain changes height in dark black. So, the effect generated would look like height lines.