How can I get my Excel icons back?

I have a MacBook Pro (Retina, 13-inch, Late 2013) that I just updated to Sierra. After the update, most of my Excel files appear to have lost the Excel icon.

All of the files seem to display the proper icon when I view folders in Column view, but in Icon view, the Excel files are white.

When I "Get Info," there is no icon showing in the upper left hand corner.

I have restarted a couple of times with no change.