According to Kerry's Island Kitchen:
There is a very real and scientific reason why eggs turn green: it is due to a reaction between the hydrogen sulfide in the egg white with the iron in the yolk to form iron sulfide, a harmless but unfortunately unappealing gray/green compound. It is this same compound that can form a gray skin around the yolk of hard boiled eggs, usually when you are trying to impress company with your deviled eggs. This reaction occurs because eggs are cooked for too long at excessive temperatures, and held for too long over heat before serving. For this reason, you shouldn’t ever actually boil hard-boiled eggs, but simmer them until they are done, then immediately cool them under cold water. With scrambled eggs, obviously you can’t douse them in water before serving, so here are a few recommendations. Cook scrambled eggs in small batches and don’t hold them for prolonged periods of time. Use stainless steel utensils (aluminum itself produces a gray/black metallic oxide when in contact with low-acid foods or boiling water). If you must hold scrambled eggs for any length of time, keep them from direct heat by using a pan such as a chafing dish which allows your serving pan to sit in warmed water, keeping it away from the direct heat source. The fresher the eggs you use, the less likely you will get greening, but that is not a guarantee
This may be of help or not.
"Food is our common ground, a universal experience." - James Beard