Colorindo tabela cor sim cor não no PHP

Codigo de professor Luis Azevedo

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Colorindo Linha Sim / Linha não - LuizAzevedo.com.br</title>
</head>

<body>

<table width="100%">

<?php    $linha = 0;
 for($i = 0; $i <= 20; $i ++){

 //Cor usada -> #33CCFF
 ?>
 <tr bgcolor="<?php if($linha % 2){ echo "#33CCFF"; }  ?>">
 <td>
 <?= $i ?>
 </td>
 </tr>

<?php $linha ++; } ?>

</table>

</body>
</html>