Instead of my pretty Faenza icon, it's using a rather ugly one.
It is a known issue.
The workaround is mentioned in the gnome-look.org Faenza page:
- Some applications are configured to always use the same icon regardless of the selected theme: e.g. vim, emacs23, gcolor2, bluefish, hardinfo, defcon, gufw, pithos, goldendict, rssowl, picasa, netbeans, gazpacho.
- To display the Faenza icon, edit as root the
/usr/share/applications/application_name.desktopfile and locate the line beginning with 'Icon='. Replace the fullpath icon name by the one of the Faenza icon (usually, it's the name of the application itself) without the extension.
- Don't forget to make a backup before changing one of those files.
- In some cases, you need to reinitialize the item in Gnome menu editor to display the new icon.
- Vim desktop file is