What causes egg yolk color to change?

The color of an egg yolk is primarily influenced by the diet of the hen. Different feed components can impart various pigments to the yolk, resulting in a range of colors from pale yellow to deep orange. For instance, diets rich in carotenoids, such as corn, marigold petals, or other plant materials, enhance the yolk's color due to the pigmented compounds they contain.

The other factors listed have some influence but are not the primary cause of yolk color change. For instance, while storage length and conditions can affect the quality and freshness of the egg, they do not alter the intrinsic pigmentation of the yolk itself. Shell color, on the other hand, is determined by the breed of the hen and does not impact yolk color, as it is separate from the feed-related pigmentation process.

Therefore, the most accurate explanation for the variation in egg yolk color lies in the alteration of the feed provided to the hens, making it a key factor in determining the final hue of the yolk.