easy, as tochjo said. In a conversation window type /nick (hold ctrl and hit k, then a list of colours will come up. choose a colour) [#or colour will appear here] Nicname so it will be like such:
/nick2 (box from ctrl+k)# Nickname.
Do this all in a conversation window, no need for copy and pastes
Edit: sorry guys, didnt know you posted it again after he asked how to use /nick.