The black discoloration seen in dry gangrene is primarily due to:

The black discoloration in dry gangrene results from ischemic necrosis leading to the breakdown of hemoglobin within the affected tissues. As the tissue dies, red blood cells rupture and hemoglobin breaks down into dark pigments like hemosiderin and other iron-containing compounds, causing the characteristic black color. This is a hallmark of dry gangrene where there is no bacterial involvement or infection, differentiating it from wet gangrene. Recognizing this pigment change is important for surgical decision-making, especially in determining the viability of tissue and planning debridement or amputation.

Reference: Robbins Basic Pathology, Kumar, Abbas, Aster, 10th Edition.