$i = 1;
foreach ($categories as $category) {
if ($i%2 == 0) {
	echo "<tr><td>".$category->id."</td><td>".$category->name."</td><td>".$category->description."</td></tr>" ;
	$i++;
	} else {
	echo "<tr style=\"background-color: grey;\"><td>".$category->id."</td><td>".$category->name."</td><td>".$category->description."</td></tr>" ;
	$i++;
}