I tried a few variations out with a black floor in the scenic model.

In this rendering, I have darkened the marble a bit on the platforms. This reduces the contrast with the floor so that it’s not so overpowering.
This is the marble that I mapped onto the platforms. It works well with the portal.
This rendering shows the same type of marble with one extra change. The platform facings are black. The rolling counter unit is still all marble, but the static platforms now look like two-inch slabs of marble on black bases. The top of each platform is painted as marble, and there is a two-inch strip of luan or Masonite framing the top of every platform and step.