Function to compare two colors by RGBa.
function colorsAreEqual($color_a, $color_b) {
// Fully transparent pixels are equal, regardless of RGB.
if ($color_a[3] == 127 && $color_b[3] == 127) {
return TRUE;
}
foreach ($color_a as $key => $value) {
if ($color_b[$key] != $value) {
return FALSE;
}
}
return TRUE;
}