[c=10]Test[/c] would make the world Test show up in colour with ID 10
Doing so in the nick would make your nick as get the same effect.
You can set your nick like this in two ways.
a) go into the WLM options to change nicks and type out the bbcode/irc code yourself.
b) in a chat window type /name followed by the name you want in the colour you want
You can also use gradients in words/nicknames by doing something like this
[c=5]This is a test gradient.[/c=20]
The same would work in nicknames