What causes variability in egg yolk color?
The color in egg yolks and the skin of yellow skinned breeds of chickens comes from the pigment called xanthophylls which is found in green plants and yellow corn. If hens are fed a ration that has very little of these ingredients, their yolks will be a light yellow in color and vice versa. Variability of yolk color in a flock can be due to disease and from hens fed free choice which causes variability in the intake of pigmented ingredients between hens.