Sorry, didn't got it right.
Look into all templates named like conversation...
but that should be a little more tricky... have to change the class in code if conversation userid is in usergroup 5 or 6 and make new css-stuff for that staff-class...
This is what I found right now... but I don't think there is something with $conversation['groupid'] at vb-original-code.
Code:
<vb:if condition="isset($conversation['edit_userid']) AND !$conversation['unpublishdate']">
<vb:if condition="!$conversation['userid']">
If you don't find anything in the code or forums you could ask again and I will think about.
If you find something it would be nice to share it. ;-)