What you see: An unappetizing sewage green hue to your egg yolk
What it is: Just some sulfur and iron compounds
Eat or toss? Eat! It’s overcooked, but harmless
Pity the hard-boiled egg! When eaten in public it can create socially uncomfortable smells. And how embarrassing to be peeled and split open, only to reveal that your once luscious yolk is now a sickly shade of green. But, worry not, egg consumers. This is just some harmless chemistry. According to FoodSafety.gov, when you boil an egg for too long, sulfur and iron compounds react on the surface of the yolk, creating this icky color. Or, this might happen if there's a high iron content in your cooking water. But, that’s it. This is safe to eat. You'll just need to decide if you'd like some ham with your, you know, green egg.
And, even better news: there's a way to avoid the green hue altogether. Follow this recipe from TheKitchn for perfectly boiled eggs (it's all in the wrist—turning the heat off is key.). I've never looked back.
Egg Safety Center