When you first click on "Multiplayer" you then click on Create which is down in the middle of two other buttons. You type in a name as it prompts, then you tell your friend to type "/join name" without the quotation marks, replacing name with whatever you typed in.
He will then be in the same room as you if you are in there.
You will have an @ in front of your name, showing you are an operator of the room.
I believe there is a list of commands, but I'm not so sure how to access it.
And with the colour thing, I can't help you. Sorry.