WpRecipes.com - Daily recipes to cook with WordPress

Edit the comments.php file from your theme. First, find the following line:

<?php if ( $comments ) : ?>

Once you found it, replace the comment loop by the following code:

<ul>
<?php $i = 0; ?>
<?php foreach ($comments as $comment) : ?>
    <?php $i++; ?>
    <li id="comment-<?php comment_ID() ?>"
    <?php if($i&1) {
        echo 'class="odd"';
    } else {
        echo 'class="even"';
    } ?>>
<php endforeach; ?>
&lt/ul>

The above code automatically ad a css class to each comment. You guessed it, we now have to edit style.css and create two nice styles for our comments.
You can use this code, for exemple:

.odd {
    background-color: #fcf9fc;
}

.even {
    background-color: #616161;
}

That's all, your comments now appears with alternated background colors. Nice, isn't it?

Credits goes to WordPress Garage for this awesome recipe!