The Christophe Robin Shade Variation Mask — Warm Chestnut ($18-$53) and Christophe Robin Shade Variation Mask – Ash Brown ($18-$53) help hair colour look its very best. For example, colour-treated chestnut hair can turn a dull brown over time, and natural chestnut hair can become ash-toned. But then natural or colour-treated, cooler-toned brown hair can turn a more brassy mahogany when something more ashy is actually desired. These hydrating masks have you covered in both those departments as they fix natural oxidation while colour correcting.