Persistent color coding for bookmarks/connections

[stefpix-oss]

I use Cyberduck professionally to upload photos to several different clients, and I often have multiple FTP/SFTP connections open at the same time.
It would be very useful to assign a color to each bookmark and have that color remain clearly visible while connected — for example as a colored strip, tab color, toolbar accent, or other persistent visual cue.
This would help prevent uploading files to the wrong client. For example:

• Newspaper A = red
• Magazine B = blue
• Agency C = green
  For people working with competing clients, uploading the wrong photos to the wrong server could be a serious and embarrassing mistake. A persistent color cue would provide an immediate visual check before dragging or uploading files.
  Even a simple implementation — such as a narrow colored bar at the top of the browser window inherited from the bookmark — would be very helpful.
  Ideally, the bookmark/connection name could also remain prominently visible alongside the color.
  This would be less about customization and more about reducing human error when managing multiple client connections.

[dkocher]

Duplicates #18443.