Purple shampoo can prolong color-treated hair and brighten natural blonde hair. Shop some of the best purple shampoos from Oribe, Kerastase and more.

"Purple shampoo neutralises the yellow in blonde hair, leaving a creamy to ash result ... leaving locks noticeably cooler for under ten pounds." What Katie says: "Before you have a go at me ...

What you really need? A purple shampoo. Yep, unlike darker brown hair colours, blonde hair has an annoying tendency to fade and become brassy. Thankfully a toning purple shampoo can help prevent this.