Ghost Sign - and Green Windows

Snapped this early today while wandering around downtown MPLS (before the great Duke Adventure). Not sure what gives with the green windows. Thought it made a neat image, but wasn't even curious enough to cross the street to look for clues.

I had dropped M and a friend off at "Opera Choir" and had 2 hours to kill. After the farmers market I wandered around and snapped a few pictures.