AwesomeWM: Trasparency issues

I have the problem that xwininfo shows Depth: 24 for any window, including the X root window. If I understand correctly, this prevents showing transparent parts of windows, such as rounded corners of tooltips, GTK+ 3.0 apps with client-side decorations etc. compton automatically starts up via rc.lua script. xdpyinfo shows visuals with depth of 32 planes. Is there a way to use 32-bit color depth, so transparent and semi-transparent windows would show correctly?