Abstract Factors affecting co-pigmentation of anthocyanins with chlorogenic acid in aqueous solutions were studied. The anthocyanins used were cyanidin 3,5-diglucoside, malvidin 3,5-diglucoside, cyanidin 3-glucoside and malvidin 3-glucoside. The variables studied were concentration of anthocyanin, concentration of chlorogenic acid, pH, temperature, and solvent. On the basis of visible absorption spectrometric measurements, a mechanism for the co-pigmentation/complexation of anthocyanins with chlorogenic acid is established. This mechanism involves formation of 1:1 pigment-co-pigment complexes forced together by hydrophobic interactions. Indeed, the extent of the pigment-co-pigment association is under the control of the unique hydrogen-bonded molecular structure of liquid water, and is affected by pH, temperature and composition of the medium.