Comment 8 for bug 1285783

same thing here under Ubuntu 14.10
gtk3 widget factory, gnome-tweak-tool and gnome-control-center backgrounds (some of the listed items) are transparent under gnome-fallback, and turn to black under gnome-shell. Even the second tab "resources" in gnome-system-monitor is transparent.
I turned the theme from Ambiance to Adwaita but the problem persists.