Aquachic: This finish is a stucco product applied over the backer board. You do thinset scratch and brown coats, then two finish coats with the stucco using a pool trowel to achieve a smooth surface. I just completed a very similar shower and used a product called called "Super Shower Finish" made by Merlex Inc. It's basically a Portland cement combined with a polymer powder to make it waterproof.
Q
I like the door! (And the view)
Q