Do you know that your hair has several colors? It sure looks like a single color, but in reality, several tones are mixed in order to reach the final result. To make any bleached hair look natural, a yellow base tone is used underneath the visible shade. If blonde dye starts to fade, this yellow base appears and hair becomes brassy.
To neutralize brassiness and get rid of yellowish tone it’s recommended to use purple shampoo whose action is based on the color theory. If you look at the color wheel, you will see that violet is directly opposite to yellow, and opposite colors are able to neutralize each other when they are mixed.
Thanks to this effect, the violet pigment of purple shampoo prevents your hair from being yellow hair by balancing the golden base tone appearance.