[imagecolorset] qrcodeでQRコードを生成した後、黒色のQRコードを青色に変更したいと思います。

<?phpinclude "../qijiang/phpqrcode.php";if(isset($_POST['addSub']) && $_POST['addSub'] =='生成二维码'){$url="BEGIN:VCARDVERSION:3.0FN:".$_POST['chineseName']."NICKNAME:".$_POST['englishName']."ORG:".$_POST['companyName']."TITLE:TEL;TYPE=work:".$_POST['officeTel']."TEL:".$_POST['tel']."EMAIL:".$_POST['mail']."END:VCARD";  $filename_temp ="card.png";  $errorCorrectionLevel = 'L';  $matrixPointSize = 2;  QRcode::png($url, $filename_temp, $errorCorrectionLevel, $matrixPointSize,4);$img = file_get_contents('card.png');$im = imagecreatefromstring($img);$indexColor=imagecolorexact($im,0,0,0);//echo "<script language='javascript'>alert('".$indexColor."');</script>";imagecolorset($im,$indexColor,0,0,255);  echo "<img src=\"card.png\"><br/>";}?>