The African black rhinoceros is the only animal whose milk is black. The milk of this female

 

The African black rhinoceros is the only animal whose milk is black. 

  Reported by Sanchita Chatterjee: 

The African black rhinoceros is the only animal whose milk is black. The milk of this female rhinoceros is dark in color due to its high calcium and phosphate content and is very thin, like water, with very little fat.