copy paste from google:

The green color in your corn flakes topping after baking is a harmless, natural chemical reaction (chlorophyllin formation) that typically occurs when a plant product (like corn, which contains chlorophyll or chlorogenic acid) comes into contact with an alkaline ingredient, most often baking soda. The reaction intensifies as the food cools down. 

To avoid the green color, you can modify your recipe to be more acidic or use an alternative leavening agent. 

Solutions to Prevent Greening

Reduce the baking soda/powder: The most effective solution is to reduce the amount of baking soda or baking powder in the overall recipe. SunButter, a company that deals with a similar greening issue in baked goods, suggests reducing the amount by about a third to a half to balance the pH.

Add an acid: Incorporating an acidic ingredient can lower the pH of the mixture and prevent the reaction.

Add a splash of lemon juice or vinegar (if it makes culinary sense in your recipe).

Use acidic dairy ingredients like buttermilk, yogurt, or sour cream.

Use aluminum-free baking powder: In some cases, baking powder that contains aluminum can cause a metallic taste and blue/green discoloration when reacting with certain ingredients. Switching to an aluminum-free brand, such as Rumford or Bob’s Red Mill, may help.

Mix ingredients thoroughly: Ensure that all leavening agents are mixed evenly throughout the entire recipe, so there are no concentrated alkaline pockets. 

Note

The green color, while potentially unappetizing in appearance, is perfectly safe to eat. It is purely a cosmetic issue caused by a natural chemical reaction.