Well you can't set specific once's to be shown, if im correct on newthread it picks random ones, and thats exactly what it does here.
As for changing the background, edit the template "chat_iframe"
Find:
Underneath Place:
Code:
<style type="text/css">
<!--
body {background-color:#ffffff;background:url();}
-->
</style>
Find:
Code:
<body class='alt2'>
Replace With:
Save the template, change the color #ffffff (thats white) to whatever you want.
- Zero Tolerance