I’m not familiar with Thunar neither, but both gnome “files” and KDE “Dolphin”’ allow you to set individual folder icons.
- Gnome: Right-click and set a custom folder icon from anywhere (usually
/usr/share/pixmaps
) - KDE: ensure the folder contains at least one
.png
or.jpg
file and the folder will display that icon.
E.G. My logs directory below contains a CD icon on top of the logs themselves:
Or am I misunderstanding your need?