Yolk colour depends on the hen’s diet. The nutritional value of the egg, however, is not affected by the yolk colour.
Free range chickens do not have strictly regulated diet like the commercially grown chickens. They do not rely on commercially prepared feed mixes, so depending on the season their diet varies and so does the colour of their yolk.
Does Yolk Colour Matter?
Yes, and no. From the perspective of nutrition, yolk colour is not an indicator of the protein, carbohydrate or other macro-nutrient levels in eggs. So egg yolk colour doesn’t matter if all you consider is the eggs nutritional value.
However, food colour does impact our enjoyment of food. Importantly, our perception of food quality is also greatly influenced by its colour.
In North America, most consumers prefer bright yellow eggs to pale ones and the commercial egg industry is well aware of this. Egg yolk colour is monitored and, in some cases, the chickens are fed supplements in order to change the colour of the yolks to make them more palatable. For example, the chemical company BASF sells Lucantin(R) red and Lucantin(R) yellow to shift the colour of the eggs to make them more yellow or more orange respectively.
As yolk colour depends on the hen’s diet, a hen that is fed plenty of yellow-orange plant pigments called xanthophylls, the xanthophylls will be deposited in the egg yolk. Hens fed mashes containing yellow corn or alfalfa meal lay eggs with medium yellow yolks, while those eating wheat or barley yield lighter-coloured yolks.
Conclusion (sort of) – pale yolk may be due to wheat and barley in the chicken’s diet, and darker yolk may be due to excessive amount of corn. Deep coloured yolks in commercial eggs may be due to artificial colorants, and local farm’s eggs may have pale yolks in the winter, and much darker yolks in the summer due to all the grass they have available.
So – know your farmer, trust your source of food. If the eggs are fresh – they are excellent regardless of the colour of their yolk.