1, purple potato porridge will turn blue-green, because purple potato is rich in anthocyanins.

2. Anthocyanin is a natural pigment, which is purple in neutral environment, purple in acidic environment and blue in alkaline environment. Generally cooked purple potato porridge and the like can easily turn blue or even green due to water or other reasons.

Just add a little acid liquid such as white vinegar or lemon juice to change it back to purple.