What are you using for the flooring in the rest of the bath?

I'd use a plain white or blue tile on the shower walls. The floor is so beautiful and intricate that you want to feature it, so don't use anything to compete with the floor. Marble on the walls is impractical as well as pricey.

Are you OK with the many issues of marble? Marble on a shower floor is the biggest problem possibility.

White ceramic tile for the walls in a plain shape (subway, square) so the floor stands out.