The green color you see in your hair after swimming in a pool is likely caused by a reaction between the copper in the pool water and the chemicals in your hair, such as chlorine or bromine. Copper is a metal commonly found in plumbing materials, and when it comes into contact with chlorine or bromine, it can form a compound called copper chloride or copper bromide, which can deposit on your hair and give it a greenish tint.

Here's a simplified explanation of the chemical process:

1. Copper ions (Cu2+) are present in the pool water due to the corrosion of copper pipes or other copper surfaces in the pool system.

2. When you swim in the pool, your hair comes into contact with the copper ions.

3. The chlorine or bromine in the pool water reacts with the copper ions, forming copper chloride (CuCl2) or copper bromide (CuBr2).

4. These copper compounds can then bind to the proteins in your hair, particularly keratin, which is the main structural component of hair.

As a result of this chemical reaction, your hair may take on a greenish or bluish-green color. The color can be more noticeable in lighter-colored hair, such as blonde or gray hair.

To prevent or reduce the green color in your hair after swimming, there are a few steps you can take:

1. Rinse your hair thoroughly with clean water immediately after swimming to remove excess pool water and chemicals.

2. Use a clarifying shampoo to remove any residual copper or chlorine from your hair.

3. Apply a leave-in conditioner or hair mask to help restore moisture and prevent the hair from becoming dry and brittle.

4. Avoid swimming in pools with high copper levels or prolonged exposure to chlorinated or brominated water.

If the green color persists, you may need to consult a professional hair stylist for treatment options or consider using a specialized hair product designed to remove copper or correct color issues caused by pool chemicals.