You have your nice adsense unit but you want to center or you want to give it a nice background.
Really simply fix but ill document it either way.
To centre the adsense unit you can use a div or a table, div is better but ill do both.
Centre Adsense with a div
Copy the code below replacing the adsense code with your own
<div align="center"><script type="text/javascript"><!-- google_ad_client = "ca-pub-121212121212121212"; /* Menu */ google_ad_slot = "12121212121212"; google_ad_width = 728; google_ad_height = 90; //--> </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script></div>
That will centre the adsense unit in the area you put it as seen here..
Centre With A Table
If you want to change the color behind the until you can use a table to do so. See the code below and replace your adsense code.
<table width=”966″ border=”0″>
<tr>
<th bgcolor=”#cccccc” scope=”row”><script type=”text/javascript”><!–
google_ad_client = “ca-pub-121212121212121212”;
/* Menu */
google_ad_slot = “121212121212”;
google_ad_width = 728;
google_ad_height = 90;
//–>
</script>
<script type=”text/javascript”
src=”http://pagead2.googlesyndication.com/pagead/show_ads.js”>
</script></th>
</tr>
</table>
As seen here…
Set the table width to be the size you want and you will see I use the colour of #cccccc , to find your colour use this app… http://www.colorpicker.com/ and copy your code.
Job done, simple!