he discolouration occurs due to a reaction between the sulfur and iron naturally present in eggs. It typically happens when eggs are overcooked, such as with hard-boiled eggs, or when there is a high level of iron in the cooking water. While the green colour may not be appealing, the eggs are still safe to eat and retain their nutritional value and flavour.
To avoid the green ring, quickly cool the eggs after cooking by transferring them into ice water.