The dark red to purple color in berries such as black currants, elderberries, blueberries, and strawberries and their juices, and in red and purple grapes, red wine, sweet cherries, eggplants, black plums, blood oranges, and red cabbage is from anthocyanin, a flavonoid which may help reduce the risk of cardiovascular disease (CVD), cognitive decline, and cancer. Anthocyanins are considered antioxidants however, new research finds that health benefits may result from unidentified chemical properties beyond their antioxidant capacity.
Plants produce anthocyanins particularly in their roots, stems, and leaf tissues, as a protective mechanism against environmental stressors, such as ultraviolet light, cold temperatures, and drought.
"The amount of anthocyanins in foods can vary greatly. For example, Red Delicious apples provide more anthocyanins than Fuji apples; black raspberries are a far richer source than red raspberries; and Concord grapes are a much more concentrated source than red grapes."
Webb, D. (2014). Anthocyanins. Today’s Dietitian: Magazine for Nutrition Professionals, Vol. 16(No. 3), P. 20.