Nexxus Hair Color Assure Sulfate-Free Shampoo with ProteinFusion for Color Treated Hair 13.5 oz. Nexxus Color Assure Shampoo has been specially formulated to help extend the color vibrancy of color-treated hair. Using Nexxus exclusive PROTEINFUSION blend this sulfate-free shampoo cleanses color-treated hair and helps replenish nutrients to help enhance color vibrancy. For best use apply shampoo to wet hair massage into a rich lather and rinse thoroughly. Follow with Nexxus Color Assure Conditioner for optimal results. Nexxus scientists used Proteomics studies to examine hair damage at the molecular level and found that the main cause of color loss and dullness is hair coloration.