If a farmer cannot produce chicken or duck eggs with consistently bright yellow-orange yolks, they may turn to dyes. Some will add red/yellow/orange foods such as paprika or marigold powder to the chicken feed to achieve the results they are wanting. Unfortunately these have not yielded results as consistent as using synthetic colorants (dyes). The industry calls giving these and other chemicals, vitamins etc. to animals Biofortification.
There are several common dyes/colorants to attain a yellow or pink color, used in chicken, duck, fish and crustaceans. One is Canthaxanthin. This dye is a food additive as well as a human oral suntanning agent. It is laboratory-made by several companies. It is known to affect our (human) sense organs and cause retinal changes in the human eye among other issues being tested. Apo-ester is another synthetic yellow colorant used to dye animals and their eggs. Its use is restricted in most countries to very small concentrations because the health/safety of the consumer cannot be guaranteed.
With respect to synthetic dyes in our food supply, there is some good news. Public demand is changing the landscape of this industry. “The trend towards natural food ingredients also affects egg yolk color: consumers want natural alternatives to get their preferred yolk color, and regulators are imposing ever stricter limits on synthetic additives. Natural pigments have historically had two limiting characteristics compared to synthetic ones, their lower absorption and their lower stability. Due to new technologies, some natural pigmentation products can now offer absorption rates comparable to apo ester and even higher stability – making them the optimal replacement for synthetic colorants.” (https://ew-nutrition.com/us/appetizing-eggs-natural-pigmentation/)
In case you are wondering, free range eggs can and do also contain these dyes. An exhaustive search did not turn up a clear answer as to whether or not organic eggs could contain these dyes. A “chemical free” label on a carton does not necessarily mean the chicken that produced the egg was not given food laced with synthetic dyes. Now you know! If we want to ensure clean eggs, I guess we will need to build a chicken coop.
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