Use the following PHP code to display alternate rows in different colours.  What this is actually doing is setting the class for one row to: odd, and the next row to: even.  Then in my css stylesheet I will define .odd and .even to have different background colours.  I see this as a very clean and manageable way to do this common task.

<?php
$i = 0; //Set the index to zero
//Put your code here to loop through the database result or whatever it is you are displaying
//Then display the table row
?>
<tr class="<?php if($i%2){ echo 'odd'; } else { echo 'even'; } ?>">

This same idea can be used in probably all web development coding languages with slightly different syntax.