This plugin colorize usernames according to the groups settings.
It can add groups styles to:

• forum index
  
• forum moderators list
  
• forums view
  
• search results
  
• announcements
  
• private messages list
  
• portal view
  

Plugin is also compatible with guest group style.
It's blazing fast, because replace usernames in output code, cache all usernames and data.

Official thread on MyBB.com Community


INFO: This plugin add link to author website (only for web spiders). 
If you do not want this, do not use plugin, or make donate and contact author.