Green beans cooked in tomato sauce often turn what color, and why?

When green beans are cooked in tomato sauce, they often turn olive green due to a chemical reaction known as the formation of phenophytin. This occurs when the heat causes the chlorophyll in the green beans to break down. Chlorophyll, the pigment that gives green vegetables their color, is sensitive to heat and acid. In the presence of the acidic environment created by tomato sauce, chlorophyll can lose its magnesium atom and convert into phenophytin. This not only affects the color but also changes the flavor and texture of the green beans. The olive green color is a sign that this reaction has taken place, indicating that the beans are still safe to eat but have undergone a change in appearance due to the cooking process.