From MatureAsskickers Wiki

Colored names

List of colors

1 - Red
2 - Green
3 - Yellow
4 - Blue
5 - Cyan
6 - Magenta
7 – White
8 - Gray
9 - Black

Adding color to your name

Open your autoexec.cfg and add the following lines:

   Seta ui_name "^1Sgt. Snuffy" 

The first line sets your name. The color for each letter is denoted by a "^" and number. My name, "Sgt. Snuffy", is all red letters so I only use a "^1" in front of the first letter.