Blood blister? Necrosis? Bruise (Photo)

Thank you for your pictures and questions. Yes, this does appear to be an area of soft tissue necrosis. I would make sure to show this area to your plastic surgeon and be seen for an evaluation. The area may need to be debrided and your surgeon can make recommendations regarding local wound care. It will likely take several weeks for this area to heal completely and will leave a widened scar.
Hope this helps!

Dear trin70,this type of wound is not uncommon after TT. It is usually caused by poor blood flow. I would suggest you to consult your plastic surgeon, follow your surgeon's instructions and keep your wound clean and covered. It can take few weeks or months for wound to fully heal. Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery

where its purple and presumably cold to touch.  Expect the area to progress slowly to a point where it stabilizes and demarcates.  Your surgeon will have to debride the dead tissue and initiate wound care, usually with saline moistened gauze, washing out the wound in the shower, and continue wound care.  Once the dead tissue is gone, your body will miraculously fill in the defect with granulation tissue (beefy red) and your skin eventually grows over it and this will take weeks.  Your scar will be much better than you could have ever imagined but scar revisions are often needed to improve on the final outcome.  Your surgeon should recognize this easily at your first post-op visit and if you are smoking or exposed to cold, you need to eliminate that now.  If you don't mind paying extra, you can rent a Wound VAC that would expedite your process.

I'm sorry to hear about your concerns after tummy tuck surgery. The dark area  is an area of tissue that is experiencing decreased blood flow (necrosis).  It is hard to know whether the process involves superficial and/or deeper tissues. Having said that, based on the photographs, I think I see pink tissue below the superficial darkness;  my best assessment is that the process will be superficial (partial thickness skin) in your case and you may be pleasantly surprised how good the earlier looks about two months from now.  Keep in mind however that area of compromised tissue may “look worse, before it looks better”. 
In my opinion, the most important “factor” involved  with successful treatment of the complication will be close follow-up with your plastic surgeon (or seek to follow with another surgeon in your area).   He/she will be able to monitor for signs of infection and decide whether or not removal of unhealthy tissue  and/or removal of exposed sutures is indicated.
 It is perfectly fine to leave the dry/dark tissue alone to "demarcate".  You will likely find that it will come off on its own and that you may or may not have an open wound present. If so Dressing changes may be necessary for a period of time. The open wound  should go on to heal over the course of  several weeks,  hopefully without long-term sequelae.  However, sometimes, depending on the final appearance of the scar, scar revision surgery may be helpful. Also, concentrate on a well-balanced ( good protein source) diet and avoid nicotine in all its forms.  Best wishes.