Fascinating little piece in the Kyunghyang Shinmun about black Portuguese mercenaries who served as frogmen for the Ming expeditionary force sent to support Joseon against Japanese invaders in the Imjin War.
Reference is made to them in the Annals of King Seonjo, which talks of “Sea Ghosts” with yellow pupils, black skin, goatees, and curly hair like black wool. These frogmen were apparently introduced to King Seonjo by a Ming general as frogmen from Portugal who could attack enemy ships from underwater.
And better still, a Korean painting from 1599 marking the withdrawal of Ming forces from Korea (see image in the link) shows troops who clearly look black.
Sadly, another Korean historical text complains the Ming didn’t actually use them during the war.
See also the writer’s blog here.