An oxidative hair dye system comprises a hair dye, an organometallic compound and an oxidising agent. The organometallic compound is preferably an organotitanate compound, particularly a tetraalkyl titanate or a titanate chelate. Such compounds are also useful for enhancing the substantivity of topical compositions applied to the body, which comprise one or more cosmetic and/or therapeutic benefit agents, a bonding agent having hydrolysable or exchangeable ligands, and a carrier.