/**
  * Set the image background colour
  *
  * @param array $rgb
  */
 public function backgroundColor($rgb = null)
 {
     if ($this->isActive()) {
         $this->_settings['background_color'] = is_array($rgb) ? implode(',', $rgb) : $rgb;
         $this->_imageObject->backgroundColor($rgb);
     }
     return $this;
 }