A family of people with blue skin lived for generations in Kentucky for generations. The Fulgates of Troublesome Creek are thought to have gained their blue skin through combination of inbreeding and a rare genetic condition known as methemoglobinemia. After spreading out and diversifying their genes, combined with medical treatment this condition has since disappeared.
An unrelated bluish skin condition is that of Paul Karason. A man who ingests colloidal silver, which he (and others) believe promotes health, but has a side effect of turning the skin blue.