I always complained that I could never keep hard boiled egg yolks from turning green when hard boiling them. My mom taught me a trick that will solve this problem easily. This is the way the French hard boil their eggs and they never get green yolks.

Put your eggs in the pan and cover with water. Put them on the stove and set the heat to high. Keep an eye on the eggs. As soon as the water comes to a roaring bubble, turn the heat off. Cover the pot immediately and allow the eggs to sit in the hot water for 10-15 minutes. They will continue to cook from the hot water, but they won't turn green.