Altitude Based Blending

Hi all, need some pointers.
Feel pretty stupid asking this as i cant see why I cant figure it out.

Basically, I want to have a material on a landscape that blends from one colour to another based on its altitude in the world.
I need to be able to choose the exact point the blend will occur, and the power of the blend.

Any ideas how to do this? Any help is very much appreciated!

Cheers all.

Try this: UE4 Landscape Materials - YouTube

Or this: Procedural Terrain Material (Unreal Engine 4) - Rioki's Corner