protected function convertColor(Node $node, Document $document)
 {
     $color = $node->getAttribute('color');
     if ($color) {
         $node->setAttribute('color', $document->getColorFromPalette($color));
     }
     if ($node->hasAttribute('chart-colors')) {
         $colors = $node->getAttribute('chart-colors');
         foreach ($colors as $key => $color) {
             $colors[$key] = $document->getColorFromPalette($color);
         }
         $node->setAttribute('chart-colors', $colors);
     }
 }