[kh99]

I'm not sure -> works with an array. I think maybe you want:

if($this->post['usergroupid'] == 6) {
        $this->post['is_admin'] = true;
}

also, you don't really need the plugin, you could just use this:

<div class="postrow" <vb:if condition="$post[usergroupid] == 6">style="background-color: #ddd"</vb:if>>

Another thing you can do, if you wanted to make different colors for different groups (or whatever) is that you could make a class for each one (in additional.css) where the usergroupid is part of the class name, then add a class using the usergroupid as part of it, like:

<div class="postrow postbg_{vb:raw post.usergroupid}">

and then in the css:

.postbg_6 {
   background-color: #ddd
}