Why fruit can turn muffins or scones blue?

Water soluble pigments called anthocyanins are responsible for this. Apples, blueberries, blackberries, cherries, some figs, nectarines, peaches, plums, raspberries, ruubarb, and strawberries are all fruits that contain anthocyanins. Peaches contain it only in there skin. To prevent your batter from turing blue or to help keep it from turing blue increase acidity such as buttermilk.