php - Color overlay on white PNG image with transparency -

i have following image: http://i.stack.imgur.com/mm8cy.png

what create "color overlay" effect in photoshop. need sort of code allow me change each white pixels values specified in rgb numbers ranging 0-255. have heard imagemagick class, not find anywhere, , have no idea how class. i'm trying imagefilter, doesn't work white images. here current code:

<?php $match = array(); if (isset($_get['c']) && preg_match('/^#?(?:[a-fa-f0-9]{2}){3}$/',$_get['c'],$match)){     $match = str_split($match[0],2);     foreach ($match $k=>$m){ $match[$k] = intval($match[$k],16); }      $img = imagecreatefrompng('splat.png');     $background = imagecolorallocate($img, 0, 0, 0);     imagecolortransparent($img, $background);     imagealphablending($img, false);     imagesavealpha($img, true);      //transformation code     imagefilter($img, img_filter_colorize, $match[0], $match[1], $match[2]);      header('content-type: image/png');     imagepng($img);     exit; } ?> 

i found solution. did - using photoshop - added red color overlay on image, looks this: http://i.stack.imgur.com/mvarn.png

and used following php code:

<?php $match = array(); $color = isset($_get['c']) ? $_get['c'] : false; if ($color === false) isset($_get['color']) ? $_get['color'] : false; $color = preg_replace('/^#/','',$color); if (strlen($color) == 3) $color = $color[0].$color[0].$color[1].$color[1].$color[2].$color[2]; if (preg_match('/^(?:[a-fa-f0-9]{2}){3}$/',$color,$match)){     $match = str_split($match[0],2);     foreach ($match $k=>$m){ $match[$k] = intval($match[$k],16); }      // load image     $img = imagecreatefrompng('splat.png');     $background = imagecolorallocate($img, 0, 0, 0);     imagecolortransparent($img, $background);     imagealphablending($img, false);     imagesavealpha($img, true);      imagefilter($img, img_filter_colorize, intval( intval($match[0],16) - 255 ,16), $match[1], $match[2]);      header('content-type: image/png');     imagepng($img);     exit; } ?> 

the key here substracted 255 red color value input this:

intval( intval($match[0],16) - 255 ,16) 

and changed color properly.