Ring Around The Rosies;

A dark skin for the dark-lovers. :]

Explanation: They say that it started in the Middle Ages when the Plague was rampant.
The 'ring around the rosy' referred to the marks that showed up on people's bodies, and the 'pocket full of posies' means the nosegays people would hold up to their noses to block out the stench of the dead. As we all know, the next line is 'Ashes, ashes, we all fall down', meaning that so many died, it seemed as if everyone would 'fall down dead'