Many fruits and vegetables contain pigments that change color in response to pH, making them natural and edible pH indicators. Most of these pigments are anthocyanins, which commonly range in color from red to purple to blue in plants, depending on their pH. Plants containing anthocyanins include acai, currant, chokeberry, eggplant, orange, blackberry, raspberry, blueberry, cherry, grapes and colored corn. Any of these plants
may be used as pH indicators.