If I could specularate for a moment..
I think the color is a fancy scale to bring out more contrast than grayscale. Radar return is just that and nothing else. It depends on electric (mostly) and magnetic properties of the surface, slope/roughness, and all these variables dependence on the wavelength used.
I'm guessing that the bright regions are relatively flat basins or liquid bodies. I think one can see run off channels on the darker slopes. The scan even has it's own 'stealth' region in the right-center of the image. It makes one think of scenarios of precipitation much different than our water world.