Folder Tree, dual, with active windows displaying a different background color

I'm using a Folder Tree in the dual display. Rather than having the Folder Tree display only one window it displays dual Folder Tree. So here is my issue.

The folder tree is displaying an active and inactive window. I would like the background in the active window to be a different color. In the past I have done this. But today I'm drawing a complete blank. I sure could use some help.

This may be what you want...

Regards, AB