I think you can only write coloured text in private messages, and only in the pregame lobby. And you can't see the colours yourself, only the recipient can.
So he wrote /msg felekfelek \pm\go\rl\ye \bt\gi\pm\ye \r!!!!!!!!!!!!!!!!!!!!!!!!
You used to be able to do the same thing in the general lobbies (#AnythingGoes, etc) but that seems to have been changed. You could even write "/msg #AnythingGoes \pm\go\rl\ye \bt\gi\pm\ye \r!!!!!!!!!!!!!!!!!!!!!!!!" to send that coloured message to everyone in the channel.