Argyria, the condition where your skin turns blue from too much silver intake.
The process that causes this is similar to developing black and white photographs. After the silver has gone through the digestive tract and lost/gained electrons it will deposit into the skin as silver sulfide. When exposed to sunlight, electrons to jump back on to the silver (from the surrounding materials in the skin), returning it back into the elemental form of silver which turns the skin blue.
Source: Wiki via Futurity