I wouldn't worry about a little black discoloration -- the body often deposits pigment in tissue that is frequently irritated or rubbed, such as nipples on a nursing mum. As long as there's no pain or redness, or loss of milk, I would not worry!
Triple science is not absolutely necessary but is strongly advised if you have high level 6 or levels 7's in science (UK). Only choose triple if you are really passionate about science. Remember getting two A* is better than three B's. Hope this was useful Minnie x