I just downloaded and installed Unity 5. I opened my project (developed on Unity 4.5) and after successful conversion I saw nothing but yellow stuff in editor (everything was fine when I pushed play). I downloaded Unity 5 example project - same thing, everything is showing up in yellowish colours. When I tried to create empty project issue was the same.
So, what the heck? I use Windows 7 and have my graphic drivers up to date.
Unfortunately your screenshot obscures the one piece of the Editor window that would be useful to see, but if you move the “Select Sprite” window down a little bit, does it say “Render Paths” underneath by any chance? Yellow colour indicates that you’re using Forward Rendering path.
To restore a “normal” scene view, what you probably want to do is select “Shaded” instead.