I use my Data (F:) drive as my work drive and regularly synchronize the changes to various backup drives (internal, mapped NAS drives and off-site external USB drive).
As an additional layer of warning to myself against accidentally working on my backup drive(s) I've set Red Label text to the first two folder levels.
On my internal drive, the labels I've set to the (sub) folders are reflected in the Folder tree (=Red text)
On my mapped NAS drives, the same application of labels is somehow not reflected in the Folder tree. Also when I apply the label directly to the (sub) folders in the Folder tree I notice that the label is not applied/saved.
I looked around in my Windows Sytem folder and noticed other folders having the Red text formatting that I can't switch off by resetting the label via the right mouse button context menu.
What they all have in common is the Folder attribute 'S' (Protected system file).
I don't know exactly which setting I used in the past to achieve this formatting (on purpose), but this one is properly reflected in the mapped drive in the Folder tree.
Just to be more clear and avoid possible confusion, the main issue (visible in the screenshot) is thus with the Red text labeled 'Data mgt' and 'Sys mgt' folders in the lister, displayed in grey in the Folder tree.
Are you right-clicking the drive-letter path, or doing it via the path the letter points to?
I'm guessing the NAS or USB drive doesn't support NTFS ADS. If so, the label information will be stored in your Opus config file against the filepath, and would only work when looking at the same file path (not something else which ultimately points to the same place via a different path).
Directly on the folders displayed in the Lister (right mouse click > context menu > Set Label) = Label applied/kept to the folder in Lister but not reflected in Folder tree.
Same trick in the Folder tree directly on the sub folder of the mapped drive (right mouse click > context menu > Set Label) = Label not applied/kept for that sub folder in Folder tree, but does then get reflected for that same folder in the Lister.
Which makes me think there is a tiny issue somewhere in the Folder tree.