I think this is a glitch due to using Parallels to run Rhino on your Mac. This is not a supported platform and has been known to cause all sorts of issues including display ones. Here’s a link to the supported system requirements for Rhino 5 http://www.rhino3d.com/new/admin#system
If the restore defaults for shaded mode doesn’t help as Pascal mentioned, I would suggest trying the exact same steps on one of the other Rhino installs on a colleagues machine as a test assuming they don’t use Parallels too.
The image looks like one of our emap images that gets installed with Rhino and is used with the emap command but the shaded mode doesn’t use this for adding slight reflections… that image map is of a simple horizon.