Contrary to popular belief, the greening of hair from spending a lot of time in swimming pools is not the direct cause of chlorine. Your hair turns green from the presence of hard metals (copper, iron, and manganese, in particular) in the pool water. Think about the color that old pennies turn after time or the Statue of Liberty. The chlorine in the water speeds up the oxidation process and the metals are able to bond to your hair, causing the greenish hue. While this happens to all types of hair colors, it is most visible in the people with blonde or lighter hair.