Argyria
It is an extremely rare condition in which the skin and mucous membranes turn bluish-gray to slate-gray. The reason behind this is either ingestion of or excessive exposure to silver. Silver toxicity is quite rare but few cases are still reported mostly because of occupational exposure to silver such as those individuals who work in silver mining. Other examples would be ingestion of drugs that contain colloidal silver. The particles of silver deposit overtime within the skin and mucous membranes giving them the metallic blue-gray appearance. It begins with gray-brown staining of the gums and then progresses to involve either a certain area of the skin or all of it. The skin gets stained with a blue-gray color and sometimes the sclera, nails and internal organs like spleen, liver and intestines also start turning into a bluish color. The hyperpigmentation is permanent and nothing can be done about it however sunscreen is known to prevent further pigmentation. Source: dermnetnz.org