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.
cooking.stackexchange.com/users/624/Adam Shiemke
Alternatively, the chickens may have been fed maize (corn); they market a specific maize-fed brand over here and the yokes of those eggs are a very deep yellow as well.
cooking.stackexchange.com/users/744/Boetsj
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.
See the yolk section of the Wikipedia article on eggs .
cooking.stackexchange.com/users/1138/Mr. Shiny and New 安宇
Don't know about Italian chickens in particular, but I know that when my mom's neighbors in Hungary feed their chickens the leftovers from making paprika, the resulting eggs have very dark yolks indeed.
cooking.stackexchange.com/users/2569/Marti
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.
cooking.stackexchange.com/users/20222/David Adams
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.
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This was also true in Spain.
I do know that our own backyard hens have this deep orangish color yoke because they have access to the outdoors, greens, and bugs, I think only factory farmed eggs are pale yellow
and I wonder if the EU has regulations about factory farming chickens.
cooking.stackexchange.com/users/78578/Mel
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?
Why are Italian eggs so yellow?
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<eggs>
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This can be a good sign that the chickens were fed a more natural diet and were not factory raised, but a deeper yellow or orange colour can be achieved with the addition of marigold petals, maize (corn), colourings or the leftovers of paprika production. The orange color of a yolk comes from the chicken's diet. Either they have been fed corn, or they have a varied diet with lots of food sources.
Chickens on a natural, outdoor diet will natually have orange yolks. If the chicken has been fed corn or food-coloring, then the yolks will also be very dark.