From TDN

Black Terrain Surface (Structure Visible)

If you have the terrain in TSE come up all black in-game, there's a good chance you've got an error in your PIXEL shader code. Open up the console and scroll back looking for red text errors.

Grey Terrain Surface (No Structure Visible)

If your terrain is not visible at all and the ground is a uniform grey, there's a good chance you've got an error in your VERTEX shader code. Open up the console and scroll back looking for red text errors.