$im = imagecreatefrompng('img/1.png');

$overlay = imagecreatefrompng('img/overlay/1.png');
    $color = array(255, 0, 0);
    list($width, $height) = getimagesize('img/overlay/1.png');
    for ($i = 1; $i < $height; $i++) {
        for ($u = 1; $u < $width; $u++) {
            $color_index = imagecolorat($overlay, $u, $i);
            $rgb = imagecolorsforindex($overlay, $color_index);
            if($rgb['alpha'] < 127 ){
                $color2 = imagecolorallocatealpha($overlay, $color[0], $color[1], $color[2], $rgb['alpha']);
                imagesetpixel($overlay, $u, $i, $color2);
            }
        }
    }
    imagepng($im, 'img/overlay/img.png');