Have you just cooked or are you cooking mushrooms in the same pan? I make omlette with mushrooms and those big field mushrooms and organic ones have a very dense black watery centre and discolour the rest of the food.
As others have said, I'd suspect residue on the pan. Sometimes I don't have my glasses on when I'm washing my pans (hot water steams them over so I can't see a thing) and I miss bits of yuck Nexy time I use it I get the same thing.
I actaully prefer a well seasoned wok for scrambled eggs. They clean up pretty easily and they can be heated oretty high without burning the eggs. Anyone else do this?
If you are cooking these eggs on flat top, it may not be cleaned enough. First, make sure you are cleaning it completely in the first place after each service period or day. After you scrub it with a sulfur block thoroughly and have wiped that mess clean and have a "fresh surface", go over it with a clean wet rag, then a dry rag, and then fresh oil and a dry rag and pick all that black gunk up still left behind. If it is an old grill, those scratches and nooks and crannies can really hold on to some stuff.