Why did my omelette turn gray?

I have a theory about your omelette (and sadly, no means to test it). But I think it is plausible, please feel free to point out logical errors.

I think that the unappetizing coloring is due to the creation of sulfur salts in your pan. Egg whites are rich in sulfur, as are all alliums (including chives). If you heat them enough (you don't mention whether you overcooked the omelette, but it happens often enough), the heat changes the molecules in which the sulfur is bound, and the sulfur atoms (or sulfur containing ions) are free to react with whatever they find around. If they happen to find iron or copper, they form sulfides and sulfates with them. These sulfides and sulfates have colors ranging from blue to green, and pure iron sulfide is black. A mixture of them with the yellow yolk can easily look gray, especially when the color is desaturated through the addition of white cream cheese.

You say you used a coated pan, but there are still possible sources for the iron and copper. First, nuts contain trace elements, including iron and copper. Second, yolks too contain iron (in fact, the bluish coloring on the surface of a hard boiled yolk is an iron sulfide created when the proteins in the egg white denaturated from the heat). Third, you can't exclude contamination of the ingredients (plants sometimes store metal ions from the environment).

I have no way to prove any of the above, but at least it sounds like a good working theory. But I will understand if you aren't eager to reproduce in order to investigate the effect closer.

BC,

While I love Rumtscho's highly chemical theory above and will probably use it to explain why my own cooking doesn't look right in the future, I have a more mundane explanation, based you the information you omitted from your original question (bad submitter!):

Kraft Philadelphia. I mixed the cheese, the other day, with walnut, hazelnut and chive. Straight from the fridge into the, fresh, unstirred, eggs.

The walnuts are critical here. Cooked walnuts exude a powerful blue-purple dye. Walnut sourdough bread, for example, is frequently purple inside. I think your eggs were grey because of the walnuts, and not because of beating too long, the cream cheese, or the pan.

I'm not sure if this is traditional omelette technique or not, but I always thought that you start with the beaten eggs (maybe some salt and pepper), alone, in the pan. Once it's semi-set, then additions go on one half of the omlet - cheese, cooked or raw veggies, whatever - and then as you slide it onto the plate, you fold the half without the additions over the side that does.

In any case, with less substances mixed into the actual uncooked eggs, there's less likelihood of interaction between eggs and items that might alter the flavor or appearance of the base ingredient.

I made scrambled eggs and forgot about them on the stove, when I came back the bottom was overcooked and the top was fluffy. I added nothing to the scrambled eggs and the eggs had a gray greenish color. Since it was only eggs that I was cooking and nothing was added I believe the pan is what makes the eggs the greenish gray color

I think this is a process where the iron the pan and egg combines with oxygen in the atmosphere. And the greyish color is iron oxide. Hard boiled eggs also tend to form a greyish color. I believe its the same reaction

I cooked 2 scrambled eggs in the microwve at work for 1 minute and 35 seconds and they turned out that bluish greenish gray color. In this case I think they were over cooked as the microwave at work seem to be higher power