Created attachment 4418 systemload-plugin-really-fix-transparency.patch The transparency fix in commit e22c9b78384e31720c29e71fc87ba145b21e6cce (bug #7345) is incomplete. There is another Gtk.EventBox that needs to be set invisible, otherwise the label background will not be transparent.
Applied in 2fe17f0, thanks.
*** Bug 9066 has been marked as a duplicate of this bug. ***