Mako,

This is what I use, let's call it myads.php and place it in /include/user. Then in /include/template/main.tpl add a line under footer:  <pun_include "myads.php">

<?php

switch ($pun_user['style'])
{
    case 'Cobalt':
        $bd_color = '565656';
        $bg_color = '2A2A2A';
        $link_color = '60A0DC';
        $text_color = 'D4D4D4';
        break;

    case 'Mercury':
        $bd_color = '565656';
        $bg_color = '2A2A2A';
        $link_color = 'F6B620';
        $text_color = 'D4D4D4';
        break;

    case 'Radium':
        $bd_color = '565656';
        $bg_color = '2A2A2A';
        $link_color = '60C860';
        $text_color = 'D4D4D4';
        break;

    case 'Sulfur':
        $bd_color = 'B84623';
        $bg_color = 'FFFFFF';
        $link_color = '822100';
        $text_color = '333333';
        break;

    case 'Lithium':
        $bd_color = '6C8A3F';
        $bg_color = 'FFFFFF';
        $link_color = '638137';
        $text_color = '333333';
        break;

    default:
        $bd_color = '0066B9';
        $bg_color = 'FFFFFF';
        $link_color = '005CB1';
        $text_color = '333333';
        break;
}

?>
<div style="TEXT-ALIGN: center">
    <script type="text/javascript">
    <!--
    google_ad_client = "pub-1234567890123456";
    google_ad_width = 728;
    google_ad_height = 90;
    google_ad_format = "728x90_as";
    google_ad_type = "text_image";
    google_ad_channel ="";
    google_color_border = "<?php echo $bd_color ?>";
    google_color_bg = "<?php echo $bg_color ?>";
    google_color_link = "<?php echo $link_color ?>";
    google_color_url = "<?php echo $link_color ?>";
    google_color_text = "<?php echo $text_color ?>";
    google_alternate_color = "<?php echo $bg_color ?>";
    //-->
    </script>
    <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>
</div>

Just add a switch line for each new style you add to your site.