Butterfly pea flower changes color based on the pH level of the liquid it is steeped in. When steeped in water with a neutral pH (around 7.0), the butterfly pea flowers will produce a deep blue color. When you add a dash of lemon or citric acid to the liquor, the color will change to various shades of blue that range from deep cobalt to mesmerizing azure. The color change is due to the fact that the pH level affects the acidity of the liquid, which in turn affects the stability of the anthocyanin pigments present in blue pea.