i've had free range chickens at least 40 years, and i want to pass on something i've noticed.
chickens that free range in a cow pasture, w/ plenty of cow manure to scratch and eat, will by far, have the darkess egg yolks.
my chickens when i was growing up scrathed in cow piles, and those egg yolks were so brite orange, went a few years w/out cows and the yolks lightened up a little.
when i got married we lived in a cow pasture, man those yolks really brightened up again.
now i still live in a pasture, but w/ horses, instead of cows, my egg yolks, are not near as dark, as my neighbors (1/4 mile away) and he has cows, we both feed the same feed. corn, wheat, & rice.
the only difference is his chickens spend the day scrating in cow piles in stead of horse piles, yup need to git me a few cows again.