We have seen many patents claim many quaternary ammonium and phosphonium salts as phase-transfer catalysts. But this patent by L’Oreal cites 173 specific quats and diquats for pairing with anionic dyes and optical brighteners. It is interesting to browse the eight pages of quat structures shown. David; H.; (L’OREAL), US Patent 9,839,591, 12-Dec-2017
The properties of quaternary ammonium and phosphonium cations that make them good phase-transfer catalysts include the ability to pair with anions and make them lipophilic. The cationic nature and affinity for organic materials, leads to the combination of these quats with the anionic dyes and anionic brighteners resulting in chromatic, powerful and particularly fast coloration on keratin fibers and particularly lightening coloration via an optical effect on dark hair. It makes sense.