Is there a sure-fire way to keep hard boiled egg yolks from turning green?

Cool them quickly after they are done cooking. Do NOT add salt to the water, it changes the boiling temperature and can make the egg whites tough.

How to boil eggs:

- set eggs out for a little while so they can warm up to room temperature

- put eggs in pot, add enough cold water to cover eggs by 1 inch

- bring to a boil, uncovered

- when it is at a rapid boil, cover and remove from heat

- wait 15 minutes

- cool eggs quickly, I start by running cold water into the pot, once the water in the pot is all cold, I add some ice cubes and wait about 5 minutes to finish off the job

Eggs that are about a week or so old are easier to peel. Fresh eggs are harder to peel.

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In a large pot, place an even layer of eggs to be boiled. Fill the pot with enough cold tap water to cover eggs completely by 1 inch. Next, bring to a rolling boil over high heat. Once the water is boiling, reduce heat to a low-medium boil and cook an additional 10 minutes for a "hard boiled" egg. For a "soft boiled" egg reduce the time by 5 minutes. Remove from heat and place eggs under ice cold water or in a bowl of iced water and chill promptly to help yolks stay bright yellow. Let stand for a few minutes in the cold water until the eggs are completely cooled. This is an important step which prevents the greenish "ring" from forming on the surface of the yolk over time.

All are good suggestions....You actually add salt to the water after boiling. Then cover and let stand.

This is a really helpful website: http://www.deviledeggs.com/

Adding salt and/or vinegar to the water usually helps.

YES!!!!!! Soak them in vinegar first