Firstly, welcome
Secondly, to be able to see coloured nicknames on the contact list, you will need MSN Messenger 7. This version is still a beta release and not meant for public download: it's still in (early) testing phase. Therefore, it's probably best if you don't use it yet. The release date could be around February 2005.
If you happen to have a copy of MSN Messenger 7, you can use Messenger Plus! 3.40 beta (see
MsgPlus! for Messenger 7 - 3.40.110 BETA - Updated!) to do what you want. Install it and enable the Custom Names feature. Then you can rename your contacts and give their names the colours you want them to have in the contact list.