When my sister was a little girl, her blonde hair turned green every summer. Hours in the pool made it so. Of course, any hair color may be altered by excessive summer swimming, but the chlorine in the pool is not the true cause. In the presence of chlorine, copper and other waterborne metals oxidize. Oxidized metals bind to the hair shaft and produce a greenish hue.
Science and yuck aside, these chemicals and very drying and damaging to the hair. In order to prevent broomstick-like goldilocks, my sister and I always wet our hair before getting into the pool; the hair shaft initially absorbs pure water rather than that which is chemically treated. Second, we lather our tresses in Biolage Hydrotherapy Conditioning Balm to create a protective barrier around the hair shaft.