In DO12, I had set up special colors for the tab edge and the background color of the files area if the location was either Dropbox or a different drive letter. I don't remember where in DO12's preferences I had configured those things (too long ago!), but the settings didn't translate to DO13. After some searching, I found the place to customize the tab edge color (Preferences/Folder Tabs/Edge Colors), but I can't find where to control the background color - is that still possible?
I think it's been rearranged.
Should be under Settings/Preferences/Folders/Folder Images (or something close, my UI is in french).
There you can define sets of folders by location or masks, and assign either an image or a fill color to the background.
Thanks - that was it!