A Negro patient had three keratinous cysts that were becoming progressively darker and signalled the onset of hemochromatosis. No change in skin color was noted by the patient. The dark color was shown to be melanin rather than a hemorrhage, as was clinically suspected. Such a sequence of events provided a distinct aid in detecting abnormal pigmentation in a darkskinned Negro.
Leyden JJ, Lockshin NA, Kriebel S. The Black Keratinous CystA Sign of Hemochromatosis. Arch Dermatol. 1972;106(3):379-381. doi:10.1001/archderm.1972.01620120063015