Black tissue in a wound is something to have assessed, not something to figure out at home.
With a leg ulcer, contact a doctor or nurse quickly if you notice any of the following: sudden, severe pain in the leg or foot; a foot or toes that become very cold, pale, blue, or black; rapidly spreading redness, swelling, or fever; black tissue in the wound; or new loss of feeling or sudden numbness. These signs may mean a serious problem with blood flow or infection and need urgent medical assessment.
Foot ulcers in people with diabetes are similar. Wounds that are pale, purple, or black are less likely to heal. Contact your provider if your foot ulcer is very white, blue, or black.
For surgical wounds, a wound that looks dried out or dark is one of the changes that should prompt you to contact your surgeon.
Dark tissue in a wound is not all one thing, and this page can’t tell you which it is in your case. Pressure sores covered in dead skin that is yellow, tan, green, or brown are called unstageable, because the dead skin makes it hard to tell how deep the sore is. That’s the point: color like this hides what’s going on rather than explaining it. Working out what dark tissue means is part of what an exam is for.