You don't need a color, but it actually does help out in showing what is dialog (inner or outer) and what isn't. As for how to do color, there are an assortment of colors you can use, but they all use the same code. I'll show you what I mean by putting in some color-names that are usually easily seen in the standard/default settings of the forums.
lightblueredyellowpinkorange[color=lightblue]lightblue[/color]
[color=red]red[/color]
[color=yellow]yellow[/color]
[color=pink]pink[/color]
[color=orange]orange[/color]
Some color-codes can be typed-in by using their RGB Hex values as well.
http://htmlcolorcodes.com/ is a good place to help you find a good visible color.
#FAC891[color=#FAC891]#FAC891[/color]
As with any color (Hex-value or name), make sure it can be seen on a grey or black background AND that it can be distinguished from white text when used in Preview.