It sounds like either you had bilateral nipple sparing mastectomies or had the nipples reconstructed post mastectomy. Either way, if it is something that had occurred on both sides, then I would not worry about it. Tissues change as time goes on, and color changes can occur as well. I would go for an examination with your plastic surgeon or oncology surgeon and see what they have to say. I hope this helps.
Since you are post breast reconstruction, and now nipple changes. Are the nipple the native nipples. It is better to see your doctor for proper diagnosis