What makes egg yolks orange

Egg yolks get their color from carotenoids, which are plant pigments responsible for red, orange, and yellow hues in certain vegetables and fruits. Carotenoids are found in green plant material because they absorb light for photosynthesis and protect the plant from sun damage. The reason some trees turn brilliant shades of yellow and orange in autumn is because you can see the color of the carotenoids as the green chlorophyll disappears.
Free-range chickens gain carotenoids from the grain, grass, and plants they eat. Their yolks change color because carotenoids accumulate in fat, and about a third of the yolk is fat. This means carotenoids can also color animal fat tissue – including your own. If you ate an excessively high amount of squash, you would develop carotenemia – orange-tinted skin!
So, the color of egg yolks depends on the diet of the chicken that laid them. The more carotenoids in their diet, the deeper orange their yolks will be.