Yeah, I agree with Guessgirl, definitely try them on if at all possible. I was pretty sure I wanted medium, but after trying them on I found that the tan color looked much better on my blonde, pale complexion than the brown color I originally wanted.
The coupon I used had an end date listed in 2007 on reesycakes, so it doesn't seem like it's ending anytime soon. There were other coupons too, so I'm pretty sure that even if you wait a while you'll still get the 20% off.