Green hair is a common side effect for blond swimmers. Even if you have taken pains to hide it beneath a swim cap or soak it in a homemade wash beforehand, blond hair can still turn green after getting out of a chlorinated pool. The green comes from the copper used in algaecide, a common pool chemical, and it leeches into blond hair after even the briefest encounter. There are many products available to treat this condition, and they fall into three categories.
There are a multitude of commercial products available to treat "swimmer's hair," ranging from those that only treat the green tint to those that deal with the side effects of chlorine and chemicals. If you are using it simply to treat the green, stick with a shampoo that treats the condition specifically. If you are an avid swimmer or if green hair is an ongoing problem, you might want to check out a more comprehensive product. Stay away from products that promise to tint your hair back to its normal color. These usually only mask the green, and it will come back after the product wears off.
Using tomato juice as a shampoo is one of the cheapest and most effective remedies. Use a liberal amount and massage it into the hair and scalp. Leave it on for 5-10 minutes, then wash it out and condition as normal. Some of the home remedies out there are as harmful as they are helpful, so watch out and use common sense. Lemon juice is one - it bleaches and strips hair. While the blond color will return, the hair is now more prone to damage and turning green upon further contact with pool water.
Preventing green hair from becoming a problem is, in many ways, preferable to treating it. Using a leave-in conditioner immediately before entering the pool works very well on shorter hair, but is not the best solution for longer hair. Some hair salons offer something called a "seal coat" or a "gloss coat" that seals many cuticles on the hair, which prevents the copper from attaching to it in the first place. A similar home remedy would be the "hot oil" treatments available from many drug stores. Using a combination of one of these treatments and soaking the hair thoroughly before entering the pool greatly reduces the chances of green showing up in your hair. If all else fails, you can still don a swim cap.