Why Does the Pool Turn Blonde Hair Green?

I'm not blonde, but I was as a kid. After a few weeks of summer, my hair would turn from blonde to pale green. Why? I always thought it was from the chlorine in the local swimming pool. As it turns out, the pool was the culprit, but it wasn't because of the chlorine. Do you know the cause of green swimming pool hair?
Photo: Phaedra, morguefile.com