Traceback (most recent call last):
  File "/usr/lib/mate-applets/mate-dock-applet/dock.py", line 2381, in show_act_list
    self.app_act_list.set_colours(self.get_applet_panel_custom_rgb())
  File "/usr/lib/mate-applets/mate-dock-applet/dock_action_list.py", line 178, in set_colours
    self.__title_renderer.set_property("cell-background", self.__bg_str)
AttributeError: 'DockActionList' object has no attribute '_DockActionList__bg_str'