I have an ongoing project to make posts for mental_floss articles I wrote way back when that I do not have an archive for. Here's another one.
There have always been tales of blue people in mythology, popular fiction, and in the news. Yes, blue people exist here and there in the real world.
Two conditions cause people to live and be (literally) blue. Methemoglobinemia is a condition in which the blood carries less-than-normal amounts of oxygen, making the blood appear blue. Argyria is caused by the ingestion of silver, usually for medicinal purposes. The effects of silver ingestion are permanent, and if the consumption of silver continues long enough, can be fatal. Read some case histories of blue people in this article I wrote for mental_floss in 2008.