Gconf and Dconf settings
A lot of QT applications will query GNOME's configuration databases for the icon theme settings. Under some circumstances there might be a discrepancy between the icon theme in use and the corresponding GNOME setting.
So to change the icons you might have to set the corresponding Gconf and Dconf keys first. You can do so with the following commands (replace
Faenza-Dark with your icon theme of choice):
gsettings set org.gnome.desktop.interface icon-theme Faenza-Dark
gconftool-2 --type=string --set "/desktop/gnome/interface/icon_theme" "Faenza-Dark"
It might take a relog to see the changes.
The theme names correspond with their basename in the filesystem. It doesn't matter where the theme is located. Be it
~/.local/share/AskUbuntu, in each case the Gconf/Dconf name will be
This fix will not work for all QT applications out there. Some, e.g. Clementine, have turned out to be very resilient for me and - as much as you might try - just won't change their icon theme. That's likely due to issues with how these applications detect the system theme. In other cases, e.g. Skype, the icons might be hard-coded into the binary and impossible to change.
How to change desktop theme periodically