OSX Finder artifacts visible through fullscreen game

I went through the Roll a Ball game example and built and ran it on Windows and it looks fine.

I built for MacOS and copied the .app file to my MacBook Pro, 15 inch early 2013, with OS X El Capitan, then ran it and I can vaguely see the outlines of the Finder icons and windows through the splash screen and game graphics as it runs, as though OSX considers the fullscreen game partially translucent. Please see screenshots below. Note that the artifacts are not there when I take a screenshot from my Mac with shift-command-4, so I needed to take a photo with my phone camera to show you what they look like. I have not seen this Finder artifact behavior in other fullscreen applications. For example, I tried running a visual novel through Steam and it runs in fullscreen fine, fully opaque, no artifacts visible, so I feel like this might be a Unity rendering issue.

Has anyone encountered this before and/or does anyone know what might be going on or how to troubleshoot/fix it? Thanks!

Screenshot with phone camera. Finder artifacts (windows visible behind game on left, icons on right):

Screenshot from Mac. Finder artifacts not visible: