Yellow tones in blonde hair can be toned down through the use of purple toning shampoo. Because purple is the opposite of yellow on the color wheel, purple shampoo is an effective tool for toning down warm yellow tones in dyed or natural blonde hair.
Warm tones in blonde hair are often referred to as brassy tones, and purple shampoo is often marketed specifically to combat these brassy tones. Dark purple shampoo is the most effective tool for banishing undesirable warm tones. Although the shampoo's color is vivid, it does not actually turn the hair purple. The shampoo should be used every other day until the desired tone is reached, and once or twice per week thereafter.