I don't want a material for every object in Rhino to be imported so I turn off that check box. The default color for Rhino is black, so you can't see anything you haven't changed. It's flat black.
But the default grey shows up flat grey in raster mode. It shades nicely in render mode, but for animating you want to switch modes to raster to view movements. You can't see the shape of Anything.
Any way to fix how raster mode shows materials? There are quite a few problems with how things show up there. I'm hoping to see them addressed soon.
I realized that it's only flat if you have the "Show Environment Image" check turned Off. In raster mode it isn't reflecting the environment, it's reflecting the environment you see on your screen. I'm not sure if that's intended or not. I'm not sure why you would want to reflect only a solid color since it doesn't resemble your rendering at all, but there it is.