Some shampoo bars are safe to use on color-treated hair while there are some that are not. You can check with each manufacturer on whether or not their formulation is safe to use on hair that has been dyed. You can also check the ingredient list for sodium lauryl sulfate, sodium laureth sulfate, and sodium chloride. If it contains any sulfate, it is best to stay away from this shampoo bar as it can cause your hair color to fade.