Board Thread:Legitimate Canon Questions/@comment-4083360-20150216155535/@comment-4091815-20150216161100

Black blood is usually a sign of sickness of the body or, possibly, the mind.

We've seen it when werewolves are poisoned like Derek in Magic Bullet and Satomi's pack in Weaponized.

We've also seen it when something goes wrong with the bite from an Alpha like Jackson and Gerard in Season 2.

Scott's wound looked black in Frayed. His inability to heal was caused by a mental block.