If you have a look around, you'll find the answer.
One of Messenger Plus!'s features is colouring nicknames. To add colour to your name you go to Tools > Options (like you usually would when your changing your MSN/WLM nickname) then if you have
Messenger Plus! Live installed, you'll see a Format button. Click this and you can choose all sorts of effects for your nickname. Here's a brief explanation of how the code works:
code:
[c=4]This text is red[/c]
This text is red
code:
[b]This text is bold[/b]
This text is bold
code:
[c=4][b]This text is red and bold[/b][/c]
This text is red and bold
You get the idea. Soo.. depending on what you mean by multicoloured, you can change your name all different colours, depending on what you pick. Reply back if you need help. Good luck.