The color of anthocyaninsare depend on the acidity of the medium. Anthocyanins in butterfly pea extract had
flaviliumcation, which was unstable in the change of pH solution. The change of pH might make the change of
anthocyanins structure that led the discoloration(Fig.4). Anthocyanin (structure I), in acidic condition was red. When
pH increased (pH < 4), colorless carbinolbase (structure III) would be formed. Tautomer occurred to produce
chalcone (structure IV). At pH < 6 the structure changed into anhydrobase (structure II). Extension of conjugation
in this structure gave color change to be blue with stronger intensity and maximum wavelength at 610 nm[15].