It surprises me that makers of black/dark rigs don't see to it that the offside of the wall panel is white or some other reflective color.
I was struck by how well white reflects heat when I touched the white surface on a plastic "film" that's black on one side/white on the other. The sun-exposed black side was very hot to the touch, but its white offside was cool. The color stopped the heat transfer in those few millimeters of thickness!
Another obvious benefit would be that warmth generated inside the rig in winter would be reflected back to the interior...