Blood supply to the nipple areola complex is always at risk during a breast reduction, especially in large reductions and if the change in nipple position is significant. It appears you had some superficial sloughing of the areola and as a result lost pigment. Based on your photo it looks like it is on the road to healing. It is hard to predict the final result and how long it will take to heal. It could take weeks to months. I would check with your plastic surgeon and they will be able to address your concerns. Good luck.