Platinum Blonde Shampoo from the Paul Mitchell blonde line. It comes out a SUPER dark purple color. And it looks like it will turn your purple hair, but SURPRISE, it doesn't. What does purple shampoo do? It neutralizes yellow tones. How? Because purple and yellow are opposite on the color wheel. Aka, complementary colors.
You just leave the purple shampoo on for about 5 minutes and it does the trick. You shampoo as often as possible which for me was 2-3x a week.
The only con to this shampoo is that it's not moisturizing at all. I found my hair was extra extra dry while using it. Using a little extra conditioner helped quite a bit, and deep conditioning my hair twice a week kept it from getting TOO dry.
Overall I'd recommend this product to ANY platinum blonde. It keeps you at the blonde you want to be at with very little work.
Do you have any blonde products you can't live without?