protected function _set_stroke_color($color) {
    if($this->_last_stroke_color == $color)
      return;

    $this->_last_stroke_color = $color;

    if (isset($color[3])) {
      $type = "cmyk";
      list($c1, $c2, $c3, $c4) = array($color[0], $color[1], $color[2], $color[3]);
    }
    elseif (isset($color[2])) {
      $type = "rgb";
      list($c1, $c2, $c3, $c4) = array($color[0], $color[1], $color[2], null);
    }
    else {
      $type = "gray";
      list($c1, $c2, $c3, $c4) = array($color[0], $color[1], null, null);
    }
    
    $this->_pdf->setcolor("stroke", $type, $c1, $c2, $c3, $c4);
  }