Purple shampoo is a type of hair care product designed to counteract the brassy or yellow tones that can appear in gray hair. Purple is the opposite of yellow on the color wheel, so it acts as a toner to neutralize unwanted hues.
It is used to maintain the desired shade of gray hair, as well as to prevent yellowing or brassiness. Purple shampoos contain violet pigments that deposit onto the hair, neutralizing the yellow undertones. This results in a brighter, more vibrant gray color.