Add ^ and number, symbol or letter infront of text you want to change.

First option:
1. Join any server
2. Open console with ~
3. Type /seta name ^number+text (e.g.: /seta name ^1ni^2ck)

Second option:
1. Join any server
2. Press L
3. Change name in player setup (e.g.:^1ni^2ck)

Third option:
1. In menu click options -> game
2. Type your name in Player Alias (e.g.:^1ni^2ck)

^0 = Black
^1 = Red
^2 = Green
^3 = Yellow
^4 = Blue
^5 = Cyan
^6 = Pink
^7 = White
^8 = Orange
^9 = Grey

^j = Claret
^c = Violet
^e = Purple
^> = Dark Blue
^d = Light Blue
^u = Cyan
^f = Lighter Blue
^h = Dark Green
^< = Green
^g = Light Green
^b = Turquoise
^o = Beige
^n = Beige
^/ = Beige
^l = Light Brown
^m = Olive
^- = Olive
^k = Brown
^@ = Brown
^? = Dark Brown
^z = Orange
^a = Orange
^i = Dark Red
^+ = Foxy Red
^* = Light Grey