What Causes Grayish To Black Vaginal Discharge?

I am 32 years old, 242lbs. I've had one pregnancy resulting in once birth 12 years ago. I delivered by cecarian. I have the Merana IUD, which was incerted 3 years ago. I have a history, prior to the IUD, of very heavy, very long and exhausting periods.

For the past couple of weeks I've been experiencing a light grayish vaginal discharge.... a week ago, I had a laperscopic surgery to remove a 10cm sized cyst from my right ovary. The ovary was also removed in its entirety.

Yesterday & this morning the discharge has turned from light grey to black. There is no pain, no itching, no "cottage cheese" look to it and the odor has not changed.

Do you have any idea what this could be?