vca_button->set_fixed_colors (vca->presentation_info().color(), vca->presentation_info().color ());
vca->presentation_info().PropertyChanged.connect (master_connections, invalidator (*this), boost::bind (&ControlSlaveUI::master_property_changed, this, _1), gui_context());
vca_button->set_fixed_colors (vca->presentation_info().color(), vca->presentation_info().color ());
vca->presentation_info().PropertyChanged.connect (master_connections, invalidator (*this), boost::bind (&ControlSlaveUI::master_property_changed, this, _1), gui_context());