My sister made me an omelette earlier, and when I dug into it I noticed several blue spots inside it, resembling mold or dye. It tasted perfectly fine, but just looked odd. She assured me that they didn't look like that whilst they were raw, but I threw the rest away to be on the safe side. What could this have been?
It sounds like the yolk was overcooked in an iron pan. Hydrogen sulfide + Iron = Hydrogen and Iron Sulfide (which is dark blue to black). This is a common reaction in eggs and generally is not dangerous at all. You can even see it in hard-boiled eggs when the yolk turns a little bit green. The most dangerous thing about this might be the hydrogen which is created in the process.