Blue people with chocolate blood

No I'm not talking about smurfs, but actual people with a blue coloration. Methemoglobinemia, or Met-Hb, is an anemic condition where there is an overabundance of methemoglobin. The excess of methemglobin is due to a deficiency in the NADH Met-Hb reductase which usually prevents the spontaneous formation of Met-Hb. The blood of patients afflicted with that condition is hypoxic and dark brown. The treatment is to supply pure O2 and inject a 1% solution of methylene blue which restores the iron in the hemoglobin to its reduced state.

The condition has given rise to different blue people mythology in Kentucky, just read this story:
"Dark blue lips and fingernails are the only traces of Martin Fugate's legacy left in the boy; that, and the recessive gene that has shaded many of the Fugates and their kin blue for the past 162 years. They're known simply as the "blue people" in the hills and hollows around Troublesome and Ball Creeks. Most lived to their 80s and 90s without serious illness associated with the skin discoloration. "

The blue coloration can also be induced by ingestion of nitrites barbyturates and other chmicals, or by explosions. So be careful on Canada Day with the fireworks you've smuggled from the states...