When you post there is a place where you can change color
Look beside the bold italic and underline
buttons. You will see "size" "font" and "color". select the color you want and it brings a box to type the text you want in color, and it shows up in your post as:
EDIT: I was trying to show you what it looked like but it won't let me so I'll tell you.
Start out by hitting [. Inside of it type COLOR=whatever you want. Then finish it with ]. After your last ] type the desired text in. Then type [, then / then COLOR then ].
That is also how you enter it into your sig as well. Copy what I just posted above of what color shows up as in your post and then enter your desired color and text.
Here is a picture where you can see part of the color tab. Ignore the arrow pointing to img.