I've noticed when I've bought Italian eggs from delis here in Europe that the yolks are very yellow - almost orange. Why is this? Assume it's the hen's diet. What are they feeding chickens there?
The yellow color comes (primarily) from vitamin A in the eggs. The eggs are high in vitamin A when the chickens are fed a natural diet of seeds, vegitation and insects.
Most of the eggs that you buy in the states are factory farmed and pale because the chickens are fed a special protein mix that has a lot of corn. This makes them lay faster and more economicly, but the mix is somewhat nutrient poor, so the eggs are less colorful. This also used to happen in cows: the milk was yellow in the summer when they ate grass, but white in the winter when they ate hay and grains.
If you find good yellow eggs, that is a good sign that the chickens led a good life on a natural diet. Of course, the feed could just be doped with vitamin A to make the eggs look more yellow.
Farmers can control the colour of the yolk by controlling the chickens' diet. Some farms add colour to the chicken feed to produce different coloured yolks.
One of the most unique uses for oleoresin paprika is that it is added to poultry feed in order to give the yolks in chicken eggs a darker yellow appearance than is natural for them. Due to the fact that is is derived from natural food sources as a food colorant, in the United States, it is exempt from Food and Drug Administration (FDA) certification. It receives equally lenient treatment under European law, where it is grouped with similar colorants of capsanthin and capsorubin.
Quoting from the KCRW Good-food podcast, episode Italy comes to LA, cauliflower, and Kachka of 6 Jan 2018: the hens are feed marigold petals.