I think I'm seeing a little sap wood on the 'lighter' side. With curl, a little viewing angle change will change the appearance. The darker side could have some surface mold on it that some of the darkness might machine off. If it's the same blank, one side might be a bit more flat sawn and could show as wider mineral streaks that might change as it's machined. It has a bit of the look like there might be a little bark inclusion above the wrist on the 'show' side? Who knows, maybe ask for more pictures? I'd think both side would likely have the same quick treatment for pictures, maybe a quick water or thinner wipe down. I couldn't see why a wood person would apply a finish to just one side, maybe?
