Why imagefill always black?

Hello guys
This is driving me mad. I would really appreciate if you told me any idea about why I see this square in red color just in my local xampp installation. If I run the code in the remote server (http://www.arreglaordenador.com/numberimage2.php) I see the square in black color instead of red. Do you have any ideas?

<?php
 
$im = imagecreatetruecolor(100, 100);
 
// sets background to red
$red = imagecolorallocate($im, 255, 0, 0);
imagefill($im, 0, 0, $red);
 
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);
?> 

Code (markup):

Thanks

 

imagefill($im, 1, 1, $red);