What discoloration occurs in eggs due to a reaction between sulfur and iron?

The discoloration in eggs that results from a reaction between sulfur and iron is specifically known as ferrous sulfide. This reaction typically occurs when boiled eggs are cooked for an extended period or at high temperatures, leading to a dark green or gray coloration around the yolk. This greenish hue is due to the formation of ferrous sulfide, which happens when hydrogen sulfide from the egg white reacts with the iron present in the yolk.

Understanding this process highlights the importance of proper cooking techniques to maintain the desired appearance and quality of eggs, minimizing the risk of undesirable discoloration. The other options listed, while related to other chemical reactions or pigments, do not pertain to the specific reaction involving sulfur and iron in eggs. Ferrous sulfide is the only choice that accurately describes the discoloration process in this scenario.