It is difficult o say from just a photo. Best to be evaluated in person by your surgeon to alleviate any concerns.
With regard to the black thing, you may actually be looking at your implant... I recommend contacting your plastic surgeon urgently for an in-person evaluation.
Dr. Dan Krochmal
From the photograph you have supplied, it appears to me that the point of most tension at the T has separated a little bit and there is some underlying visible granulation tissue. I don't know of any deep black colored sutures other than nylon and those are not usually placed in a permanent position beneath the skin. There are some dark blue melt away type sutures that we use. I would recommend you go back to your plastic surgeon to be seen and have that foreign body removed. With the suture out of the way, you will heal more quickly. Congratulations on your surgery.
Thank you for your question and for sharing your photograph. I can see your area of concern and I would see your surgeon for an in-person evaluation. Necrosis has unfortunately already occurred causing the delayed healing of your incisions, and If the stitch was removed completely, the dark area may be the bottom of your implant. Call your surgeon sooner than later. Hope this helps.
You shouldn't be seeing stitches or black- I recommend that you have your wound evaluated in person by your Plastic Surgeon as soon as possible.
All the best
My concern is that your implant may be exposed-please see your surgeon immediately. I do not see a stitch.