Final answer:
To correct a greenish cast in blond hair, you can use a purple or violet toning shampoo/conditioner or seek professional help from a hair colorist.
Step-by-step explanation:
In the context of hair coloring, a greenish cast in blond hair is often caused by chlorine or copper compounds in swimming pool water. The simplest way to correct this greenish cast is by using a product that can neutralize or counteract the green tones. This is typically achieved by using a purple or violet toning shampoo or conditioner.
These products work by depositing a small amount of purple pigment onto the hair, which helps to cancel out the greenish color. When used regularly, they can help to restore the desired blond shade by neutralizing the unwanted green tones. It's important to note that these products should be used in moderation and according to the instructions to avoid over-toning the hair.
Another option to correct the greenish cast is by seeking professional help from a hair colorist. They have specialized knowledge and access to professional-grade products that can effectively correct the color imbalance in the hair.