Welcome Background

[Paper Box]

Forum URL: dotj90.proboards84.com

I'm having some trouble and it is this.
Whenever I go to edit my skin/forum colors, I can't find the welcome table background, and then on the bottum of each post it's purple just like the welcome table background. I want to make it this (http://haef.szm.sk/backgrounds/blue_800600.jpg)
How would I go about doing that?

Help appreicated and thanks in advanced.

[xiØn]

Welcome Table Background Image

<style type="text/css">
<!--
.welcomebg {background-image: url(URL OF IMAGE); background-repeat: repeat;}
-->
</style>