Center panel background color different in output than preview

We published a project in April with the center and right panel background in a light gray and now, even tho the skin edit preview shows the light gray, the frameless published help has a distince white center panel where the topic content displays. We have the TOC on the left and mini TOC on the right. There is a home page with tiles that renders correctly. 

The RoboHelp project samples show the same issue. Does somebody know why this is happening and how to fix it? We've compared all of the settings and tried replacing the CSS and skin with the one that worked and it's still a problem. 

Any help is appreciated!