At certain pH levels, some colorants degrade or shift to a different, less-stable color.
Most synthetic dyes have good low-pH stability; however, Red No. 3 will precipitate at a pH less than 4.0.
Lakes are stable at a pH between 4.0 to 8.0, but outside that range, a lake’s substrate typically breaks down, releasing the dye and causing color migration.
“In the natural colors, annatto will precipitate at a pH less than 4.0, and carmine breaks down at a pH less than 3.5; however, these colorants can be used in acidic applications by modifying their form. For instance, an annatto emulsion resists precipitation at low pH.
The anthocyanins are most stable and supply red hues at pH less than 3.8, while at higher pH levels, the color is either lost or shifts to unstable blue and/or purplish tones.