Which Came First? The Chicken Color or the Egg Color?
Pearly white, cream, yellow, brown, gray, blue, violet, green, olive. Chicken eggs are colorful even before they're dyed and decorated for Easter celebrations. "The color of eggs comes exclusively from the pigment in the outer layer of the shell and may range from an almost pure white to a deep brown, with many shades in between. The only determinant of egg color is the breed of the chicken. . . . A simple test to determine the color of a hen's eggs is to look at her earlobes. If the earlobes are white, the hen will lay white eggs. If the earlobes are red, she will produce brown eggs" (David Feldman, Why Do Clocks Run Clockwise? and other Imponderables, 1988.
Poultry expert Katie Thear notes that "All eggs are initially white, and shell color is the result of the pigments called porphyrins being deposited while the eggs are in the process of formation. In the case of the Rhode Island Red, the brown pigment protoporphyrin, derived from haemoglobin in the blood, is what gives the shell its light brown color. The Araucana produces a pigment called oocyanin, which is a product of bile formation, and results in blue or bluish-green eggs. Interestingly, the color goes right through the shell, making the eggs difficult to candle [i.e., test for freshness by holding up to the light] during incubation."
Interestingly, the light of the sun can fade the color of an egg's shell, even before it has been laid. This is a phenomenon that especially affects free-range chickens in hotter climates. "Although shell color is mainly determined by genetics, the effect of strong sun and high temperatures on the hens can produce a fading effect on the shells. Why too much sun affects the surface pigmentation in this way is unknown, but it can be a problem for those who sell such eggs," Thear says. She notes that stress, premature laying, changes in diet, bullying, viral infections, and the presence of predators can also lead to eggs with pale colors.
[Read the entire article in my guest blog at ColourLovers.com.]