Purple potato will turn the cooked porridge into purple when it is cooked, especially when millet is cooked. Millet itself is golden yellow. According to the superposition of colors, adding purple to gold will make purple darker. Baking soda is weakly alkaline. When it is dissolved in water, it will produce bubbles. A small amount of baking soda is harmless to human body. Therefore, to sum up, the color of purple potato millet porridge with baking soda will definitely become darker, which is harmless to human body and will not cause chemical reaction.