Blue shampoo won't turn your hair blue. But what it can do is help fight the stubborn brassy, orange tones that can make brunette hair lose its luster. Think of it as simple color theory: the same way that purple shampoo can help brighten blonde hair by counteracting yellow tones, the same is true for blue shampoo and brown hair's orange tones. A great blue shampoo will help extend the quality of your hair color between salon or color appointments without accidentally redecorating your entire bathroom. Ahead, the 8 essential blue shampoo formulas for all hair types.