Meet the real world equivalent of fictional blue-skinned Andorian [wiki] of Star Trek: the blue people (whose skin color is caused either by a hereditary blood disease or ingestion of elemental silver).
From The Human Marvels:
Argyria is an extremely rare condition caused by the ingestion of elemental silver, silver dust or silver compounds and the most dramatic effect of argyria is that the skin is colored blue or bluish-grey. The most famous person with argyria was Captain Fred Walters. Walters was born in England in 1855 and was a captain in the British army before a degenerative neural condition, locomotor ataxia, prompted his retirement. Treatment for his condition included the ingestion of silver and that regular ingestion caused Captain Walters to turn blue. He subsequently traveled to the United States in 1891 and began a career exhibiting himself for profit.
As time went on Walters allegedly increased his silver intake in an attempt to turn himself as blue as possible. For awhile, he was successful and his deep blue pigmentation resulted in more fame.