Don't know how it actually works, but my bet it's in the format:
</color_tag>your_colored_text
the </FFFF00> part is there to switch color back to yellow as it is. If you don't append it, all the text following color tag will be in that color.
Here

are all codes you should be able to use safelly.
So, if I make </FF33FF>Kick </0000FF>da </FF0000>Bunny </000000>...MrBlacky
it would look like
Kick da Bunny ...MrBlacky
[/1/0=AuctionItem] has something to do either with:
a) hyperlinks
b) text decorations, like
bold or
underline. Try mixing them and see what comes out (whisper yourself)
may be both