Open your theme css file, and paste this at the bottom:

.color1 {
background-color: #DBDBDB;
}
.color2 {
background-color: #EEEEEE;
}

Make sure that your CSS doesn’t have a style that will overwrite this coding.

If your theme has a color for #commentbox, just as an example, then you must remove the background-color line. If you don’t, then the change won’t happen.

Then open your Comments.php file. Make sure to create a backup prior to making any changes to this file.

At the VERY top of this file, put this on a line of it’s own.

<?$i;?>

Now scroll down to find this part of the code:

<?php foreach ($comments as $comment) : ?>
<div>
<div>

if you do, change it to:

<?php foreach ($comments as $comment) : ?>
<div id=”commentbox”color1″:”color2″;$i++;?>”>
<div>

Or you might have something like this:

<?php foreach ($comments as $comment) : ?>
<li id=”comment-<?php comment_ID() ?>”>
<?php comment_text() ?>

if you do, change it to:

<?php foreach ($comments as $comment) : ?>
<li id=”comment-<?php comment_ID() ?>”color1″:”color2″;$i++;?>”>>
<?php comment_text() ?>

You need to add the class of css to the above.

Your theme might not have these specific lines, but you need to do the next change in the same area of comments.php. If you cannot figure it out, post to the Support Forums but you MUST say what theme you are using. Without that information your chances of an answer are zero.