Short explanation of colour codes..
Say you wanted red writing.. you would put [c=4] at the beginning and [/c] at the end. Then you can do another colour, for example [c=7]text[/c] for orange. All the colours are in the Format Panel and you can find the number of the colour there.
Best way to customize your name is to open up a conversation and type /nick followed by your nickname. You can highlight what text you want to change colour, click the Format Panel button and choose the colour. Then highlight a different piece of text and choose another colour. Do the same thing for background.
Here's a quick animation explaining how. Press enter once you're done and it will change your name.
Note: I'm using a skin so the buttons, etc. are different