Germ contamination and controversial dyes: How healthy are colored eggs from the supermarket?. In Germany, only dyes approved for use in food may be used to dye eggs.
Organic eggs may only be colored with natural dyes and treated natural coatings. Natural dyes on loose eggs can also be problematic for sufferers of allergy. In some eggs the yolkish discoloration does not pose a health risk. It occurs when the egg is cooked for more than ten minutes and reacts with sulfur compounds from the white.