There is a link to a "Using Markup" guide at the top of the text box when you go to reply to a thread. It thoroughly explains the different times of markup and how to use it.
Also, if you click on the colour wheel above the text box when you try to reply to a thread, it will set up a colour markup for you (you will have to replace "null" with your choice of colour, and then type the text you want to colour between the "][" ).
Hey, Holo, the site listed in that guide has been shut down for quite some time.
Beast, because of that, the process is a bit more tedious. Unless someone can suggest another website that does the same function, you have to do it manually. There are also sites with hexadecimal codes, which dictate the ratio of colours in a produced color (Think of it like mixing paint!), listed in Holo's referenced link that you can use to generate a variety of colors. The one I like is www.0to255.com, but it's purely personal preference. There are THOUSANDS of websites on this and many of theme will even try to help you generate entire colour schemes, many of which come out absolutely stunning.
FYI, how I created this: [color=e01671][b]H[/b][u]ope[/u][/color] [color=f7ec86][b]I[/b][/color] [color=20abe2][b]h[/b][u]elped[/u][/color][b][i]![/i][/b]
"Oh, you're right. I hadn't realized that the website was down. Thanks for catching that!"
It's been down for a while. The commonly used livemarkup.co.nr is down too and is now livemarkup.heliohost.org (the co.nr is a URL replacer that probably expired.) Livemarkup is still very useful and is worth including in an updated version of that guide.