 This Old World monkey's coat ranges from dark red to black, accented with a black stripe along the shoulders and arms, and a pale underside. Its black face is crowned with long, white hair, and features a distinguishing pink mark on its lips and nose. Also, the Zanzibar red colobus has a long tail used only for balancing — it is not prehensile. Sexual dimorphism is generally decreased in the species, meaning the females have little difference in their body size and colour from their male counterparts. Females usually outnumber the males in their groups. The species has a notably small cranium and rotund body shape, with males potentially reaching over 12 kg and females, 10 kg. In adults, highly differentiated facial features help them to distinguish each other in a group.
