Your contacts font or font-colour isn't available from the Messenger Plus! Scripting. You've got to apply your own hooks (either RichEdit or Socket), using a DLL.
There's an addon for Windows Live Messenger that does this, MessengerDiscovery Live. This addon has a few bugs, and I don't recommend really it, because it's built for older versions of Windows Live Messenger.
However you can use it in group chats and it will use your contacts font and font-colour, as you wanted.
Download it at your own risk at
http://live.msgdiscovery.com/.
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