it is a fixed function effect, not a shader. if you want to understand how to make a very similar shader, you can check the ones in MapBuilder. there are better ones too (e.g. an auto terrain shader based on height and slope, with two additional textures that can be hand-painted onto terrain for roads). moreover in MapBuilder you can tweak them real-time, thus making your learning faster, let's say 1 week instead of 7 months.