So I'm trying to setup a hook on fetch_musername

[DISLEX]

And when the user matches certain characteristics, I force-change their musername to a different style. Problem is, when I do that, it changes it for EVERYONE. Makes no sense to me...

This is the plugin on the hook:

if (is_member_of($vbulletin->userinfo, 31))
{
  $user[musername] = "<strong><span style='color: #FF66FF'>" . $username . "</span></strong>";
}

I know that I could setup a style for usergroup 31, this is only test code. I want to expand upon that if(). But the problem is, it applies this to everyone, not just the users in group 31. How is that even possible? I thought it had something to do with the goofy static $hook_code junk inside functions.php, so I replaced it with a normal hook call, but that didn't change anything.

Any ideas?