What makes egg yolks dark yellow, compared to the pale grocery store egg yolks?
Beta carotene, or xanthophyll both are natural plant pigments. When hens are able to eat green plant material or yellow corn (factory farm hens are sometimes fed yellow dye to color the yolks), the beta carotene concentrates in the yolk making it dark, sometimes even orange. Eating red peppers makes yolks red, and some plants can make the yolks green or even black.
