Lulz you can do that without a plugin. You have to assign a user rank image to a usergroup. You log into your admincp and on the left side expand user ranks like such:
Click on "Add New User Rank" and you should get a page like this:
Now you add whatever you want I'm going to set the administrator user rank like such (you can have it the way you want but this is how I do it):
(The path depends on where you put the image!)
Alright after you save it or add you will see your user rank in the manage user ranks page like such:
Also, YOU MUST COMPLETE "Update Counters" which is located at:
your-url.com/path-to-forum-or-admin/misc.php?do=chooser
Once you do some of the updates it will work for the user groups done. I suggest you add all user rank images before updating everything.
As far as the colour go you can do that in admincp as well. On the left expand usergroups and click on "UserGroup Manager".
Edit whatever usergroup you wish and in the "Username HTML Markup" box put in the HTML codes. There are 2 boxes! One for before the username, the other for after! So like if you want to make a username red,. in the first box you would insert;
Code:
<font color="#FF0000">
and in the second box you would insert:
Code:
</font>
.
Rather than typing in #FF0000 (which is the HEX code for red) you can just type in red but WITHOUT the #.