Turns out the culprit was the fact that I had:
Qt Code: 
  1. setStyleSheet("background-color:  rgb(240,240, 240)");
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in the mainDialog.cpp

This propagated to widgets that cannot be styled this way. In order to style the scrollbar, it looks like I am going to have to style each part of the scrollbar.
stylesheet description for scrollbar

I was hoping that I could set the color of my entire application in one call but it looks like I am going to have to be a little more detailed than that.