The greenish color around the yolk of hard-cooked eggs is a natural result of sulfur and iron reacting at the surface of the yolk. It may occur when eggs are cooked too long or at too high of temperature, or when there is a high amount of iron in the cooking water. Although the color may be unappealing, the eggs are still wholesome and nutritious and their flavor is unaffected. Greenish yolks can best be avoided by using the proper cooking time and temperature (avoid intense boiling), and by rapidly cooling the cooked eggs. Occasionally scrambled eggs can develop a greenish tint if over-cooked at too high of a temperature or are left too long in a metal pan.
