PHP imagecolorsforindex() function

<?php
   $img = imagecreatefrompng('https://www.tutorialspoint.com/images/tp-logo-diamond.png');
   $x = 25;
   $y = 45;
   $rgb = imagecolorat($img, 25, 45);
   $colors = imagecolorsforindex($img, $rgb);
   var_dump($colors);
?>