There are two ways to do this: I'll cover the easier one. First, you must have access to the toolbar, so you'll have to be quoting, editing, or starting a thread.
That done, highlight whatever text whose color you wish to change. On the Toolbar, you'll find a button marked "Select text color", represented by a capital A.
Click on that button to bring up the color pallete. Select whichever color you wish to make your text, and the change will be complete.