I've installed the clipboard manager diodon, a status panel applet I've used before with Ubuntu that works very well. The only annoyance is that in elementary it doesn't use a monochrome icon, but rather the default, colored icon.
I found some instructions for changing the icon manually which basically included copying the icon from
/usr/share/icons/ubuntu-mono-dark/status/22 to my own theme's icon folder. Since elementary didn't appear to have 22px resolution icons, I copied from and to the 24 folders instead. But this didn't have any effect, the panel applet icon is still the same as before, even after having run
sudo gtk-update-icon-cache /usr/share/icons/elementary/.
What am I doing wrong here?