The colorants  that give purple sweet potato color their characteristic color are anthocyanins. These colorants exhibit a 

reversible change in molecular structure as the PH of solutions change from to basic.

This change in structure is characterized by a shift in hue from red to purple red as the PH changes from to basic.

Application: 

Flavors,energy drinks,soy drinks,spirits,juice drinks,specialty tea,ice cream,yogurt smoothies,fruit preparation,salad dressing,breakfast cereal,dry mixes.