What color do onions turn when cooked in an aluminum pan?

When onions are cooked in an aluminum pan, they tend to turn a yellow color due to a chemical reaction between the onion pigments and the aluminum. Onions contain flavonoids, particularly quercetin, which can change color when exposed to various conditions, including heat and acidic or basic environments. The aluminum reacts with the compounds in the onions, leading to a change in their color. Consequently, the yellow hue that emerges is a result of this interaction, reflecting how certain cooking materials can impact the final appearance of the food being prepared. This aspect of cooking illustrates the importance of understanding how materials and food chemistry can influence culinary outcomes.