I'd like some kind of visual warning when I've got a network folder open. Any way to control, say, lister background color (or display a colored rectangle around the lister perimeter) when the lister points to a network location?
You can set Format for Network Drives.
Look at Preferences > Folders > Folder Formats, edit and check Network Drives.
Also you can read this FAQ :
Thank you. I'll read up on that feature.