private static function _get_saturation( $hex ) {
		$red   = hexdec( substr( $hex, 0, 2 ) );
		$green = hexdec( substr( $hex, 2, 2 ) );
		$blue  = hexdec( substr( $hex, 4, 2 ) );
		$max_rgb = max( $red, $green, $blue );
		$min_rgb = min( $red, $green, $blue );

		$cnt = round( ( $max_rgb + $min_rgb ) / 2 );
		if ( 127 >= $cnt ) {
			$tmp = ( $max_rgb + $min_rgb );
			$saturation = $tmp ? ( $max_rgb - $min_rgb ) / $tmp : 0;
		} else {
			$tmp = ( 510 - $max_rgb - $min_rgb );
			$saturation = ( $tmp ) ? ( ( $max_rgb - $min_rgb ) / $tmp ) : 0;
		}
		return $saturation * 100;
	}