def _shade_remaining_missing(self):
        """Helper method to shade any missing labels remaining on the current
        page. Not intended for external use.

        Note that this will modify the internal _position attribute and should
        therefore only be used once all the 'real' labels have been drawn.

        """
        # Sanity check.
        if not self.shade_missing:
            return

        # Run through each missing label left in the current page and shade it.
        missing = self._used.get(self.page_count, set())
        for position in missing:
            self._position = position
            self._shade_missing_label()