>This trick got from OMG! Ubuntu

1. Press ALT+F2 and type ‘gksu nautilus /usr/share/icons’
2. Copy the ‘ubuntu-mono-dark’ folder (for dark panels) or the ’ubuntu-mono-light’ folder (for light panels), paste it right away and then rename the new folder to whatever you like (e.g. ‘magog-white-dark’ if you use the Magog iconset and a dark panel)
3. Now edit the ‘index.theme’ file located in the pasted folder with root privileges
4. Change ‘Name=Ubuntu-Mono-Dark’ to whatever you want the iconset to be called (e.g. ‘Name=Magog White Dark’)
5. Change ‘Inherits=Humanity-Dark,gnome,hicolor’ to whatever the name of the folder (!!) containing your favorite iconset (probably located in ~/.icons) is (e.g. ‘Inherits=Magog White’)
6. Save and close the index.theme and chose the new iconset (e.g. ‘Magog White Dark’) from the GNOME appearance properties