[notrious]

Usergroup Color Bar Legend
https://vborg.vbsupport.ru/showthread.php?t=165980

OR
Custom Colored Usergroup Legend
https://vborg.vbsupport.ru/showthread.php?t=169486

OR

Use the HTML Markup function:
Admin CP -> Usergroups -> Usergroup Manager -> Edit Usergroup -> Username HTML Markup
Example

For Admins, go to the Usergroup Manager and edit the Administrator group. For the Username HTML Markup, in the first field put:
HTML Code:

<span style="color:red" title="Administrator"><b>

and in the second put: 
HTML Code:
</b></span>

For Moderators, go to the Usergroup Manager and edit the Moderator group. For the Username HTML Markup, in the first field put:
HTML Code:

<span style="color:blue" title="Moderator"><b>and in the second put: 
HTML Code:
</b></span>