how can I get alternate white/grey rows

[astoller]

What can I do with this code so that every alternate row
prints white(ffffff) then light grey (eeeeee) then white again?
& what does the echo join command do?

<h1>phoenix contact list</h1> 
<table> 
    <tr> 
        <th>url</th>     

        <th>email</th> 
        <th>Company</th> 
        <th>Category name</th> 
    </tr> 
<?php while($row = mysql_fetch_row($result)){ ?> 
    <tr> 
        <td><?php echo join('</td> 
        <td>', $row); ?></td> 
    </tr> 
<?php } ?> 
</table>

[Installer]

Here's an easy method:

$arr = array('Row 1', 'Row 2', 'Row 3', 'Row 4');
$clr = array('red', 'blue');
$sw = true;
echo '<table>';
foreach ($arr as $val) {
    echo '<tr bgcolor="' . $clr[$sw = !$sw] . '">';
    echo '<td>' . $val . '</td></tr>';
}
echo '</table>';

join()