You can blame the farmer.

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Take a chance on those free-range, farm-raised chicken eggs at the grocery store and you’ll notice the color of the yolks are often much closer to orange than yellow. But what accounts for the difference?

Watch: 4 Ways to Perfect Eggs with Blackberry Farms

What’s in an Egg Yolk

Making up only one-third of the egg’s entire weight, the yolk contains 75% of an egg’s calories. A complex bag of proteins and fats, the yolk also houses most of the iron and Vitamin A found in the cell. All of these nutrients have to come from somewhere, and a hen obtains them from different sources—here lies the mystery of the different yolk colors.

From Yellow to Gold

For a laying hen, the saying “you are what you eat” applies more to the eggs she produces than to herself. In Harold McGee's book On Food and Cooking, we learn that every year, a hen “converts about eight times her body weight into eggs” (McGee 73). Therefore, what a chicken eats has incredible influence on the composition of the eggs she lays.

Chickens that eat plants with a higher concentration of certain pigments (called xanthophylls) produce egg yolks with a deep orange color. These eggs are not more nutritious than eggs with a pale yellow yolk, they just contain more color-affecting components from the feed of the hen. Chickens that are allowed to roam tend to find and devour plants with these pigments (like alfalfa), but chicken feed made of corn will often produce a similar effect. Some farmers who are committed to selling eggs with deep colored yolks will even feed their chickens marigold petals to ensure that the yolk color is just right. (Prizing an egg with a brighter yolk is no new practice—farmers in Italy have been customizing their chicken feed for centuries to sell eggs that make for a yellower pasta.)

The next time you crack open an egg and observe the hue of the center, you can rest assured that no matter the color, you’re reaping the nutritional benefit of a hard-working chicken.

The main source for this article is On Food and Cooking by Harold McGee (Scribner, 2004).