I saw a programme the other night, where a women had just had her hair highlighted. She was advised by the hairdresser to wet her hair with tap water first, before she went swimming in a pool.
Sorry I can't remember the reasoning behind this, but it may help.
If you swim regularly I would advise wearing a cap or some protection gel. Your hair may not turn green, but the added harshness of highly chlorinated water on already damaged hair will not do it any good.