Wild colors abound in foods and can stun the unsuspecting cook.
You can be sauteing red cabbage, and you have done nothing. You are totally innocent. You are just standing there, and it turns a disgusting blue. It turns out that anthocyanins, the compounds that give red cabbage its red color, have to be acidic to stay red, and some of the acids have evaporated off. If you want to play, you can add some baking soda, and it will turn blue again.