A method for mixing substances for the treatment of keratinous substrates may comprise separating a paperboard packaging container into at least two portions. The method may also comprise removing at least two containers containing differing substances from the paperboard packaging container and mixing the at least two substances together in one of the at least two separated portions of the paperboard packaging container so as to form a mixture of the at least two substances for the treatment of keratinous substrates. The method may further comprise applying the mixture to a keratinous substrate.