What determines the color of the yolk?
Diet. It’s fairly simple to manipulate the color of an egg by adding marigolds or other foods containing xanthophylls (yellow pigments) to a hen’s diet. Eggs in the US are the color they are because that’s the color consumers seem to like. In Europe for whatever reason they like their eggs to be more orange in color. It’s theoretically possible to make an egg with virtually no color, for example by feeding a diet of white corn. There’s not necessarily a connection between color and flavor, though there can be. In the US, it’s unlawful to add food coloring as such to chicken feed — though this would be an effective strategy for coloring eggs.
