That does get me a little further, but now it still fails on the last line:

      my $l = new Gtk::Label( "Success" );
      my $colormap = $l->get_colormap();
      my $gdk_color = Gtk::Gdk::Color->parse_color( "green" );
      $gdk_color = $colormap->color_alloc( $gdk_color );
      $l->window->set_background( $gdk_color );
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$l->window is undefined, so can't do a set_background on it, and $l->set_background doesn't appear to exist either.