Greenish fluid aspirated

I had a lumpectomy in August of 2017.This was followed with chemotherapy and radiation. I was her2 positive in right breast. Ive been taking anastrizole for a couple years. My oncologist recently okayed me going off of it becausd of weight gain and joint pain and sleeplessness. Ive been feeling pretty good but depressed from weight gain. So I felt another seroma. Ive had a couple aspirations since surgery. Each time it was alot pinkish fluid. Yesterday it was greenish fluid from the aspiration. The breast surgeon said it was atypical to be getting seromas so late after surgery and that color. I'm wondering what it is. I am on antibiotics now.