Go to Users & Groups > Groups > Usergroup you wanna edit. Then at Username Style replace all the contents in there with the following:
PHP Code:
<span style="color: #FF0000;text-shadow: 0px 0px 8px #000;font-weight: 500;">{$username}</span>
change the FF0000 to color you want :3
You'll will see the username and a shadow :3. Thx k bye
make your own styles from here - http://www.w3schools.com/css/css3_text_effects.asp