We show that multireference perturbation theory based on a four-electron, three-orbital state-averaged complete active space self-consistent field model can reproduce the shift in colour between diarylmethane dyes and their corresponding azomethine analogues. We relate the azomethine shift to changes in the electronic structure, through an examination of the relative changes in the state-averaged one-electron Hamiltonian (Fock) and surprisal matrices that characterise the analogous self-consistent field solutions.