var setBackgrounds = function(evt) {
    var view = evt.event_data.data.sender;
    if (view.overlayId) {
        var incoming = evt.event_data.data.incomingView;
        if (incoming) {
            if (incoming.id.match('performance')) {
                view.setOverlayShadowImageSrc('http://images.apple.com/macosx/images/overlay_performance20090608.png');
            } else {
                view.setOverlayShadowImageSrc('http://images.apple.com/macosx/images/overlay_gallerybg20090303.png');
            }
        }
    }
}

Event.onDOMReady(function() {
    Event.Listener.listenForEvent(AC.ViewMaster, 'ViewMasterWillShowNotification', false, setBackgrounds);
});