The Egg Color Guide: What Determines Shell Color

All egg shells start white. Brown eggs are white shells coated with porphyrin pigments applied in the hen's uterus during the last 4-6 hours of shell formation. The amount of pigment applied — and therefore the depth of brown color — is genetically determined and consistent within a breed, but it fades over the laying season as the hen depletes her porphyrin reserves. The first eggs of the season are the darkest; late-season eggs from the same hen are lighter.

Blue eggs result from a different mechanism: the pigment oocyanin is integrated into the shell matrix itself, not applied as a coating. This means blue eggs are blue all the way through the shell wall. Breeds with blue eggs carry the oocyanin gene: Araucana, Ameraucana, and many mixed breeds. The Araucana is the original source — a South American breed brought to North America via Spain.

Green and olive eggs result from a brown-egg coating applied over a blue-egg base shell. An Easter Egger (a mixed breed carrying the oocyanin gene plus a brown-egg gene) lays greenish eggs. Olive Egger crosses (typically a dark brown layer like Welsummer or Marans bred to a blue-egg layer) produce eggs ranging from sage green to near-black.

Cream and pink eggs: most 'white' eggs from production breeds are precisely white. Most eggs described by keepers as 'cream' or 'pink' are pale brown with very light porphyrin coating. True pink-tinted eggs come from some Silkie and Light Sussex lines.

Does egg color affect taste? No. Diet and freshness affect egg flavor. Shell color is a genetic trait unrelated to yolk color, albumen quality, or flavor. The perception that blue or green eggs taste different is a function of freshness (most colored-egg breeds also tend to be less commercial, meaning the eggs are fresher when purchased) and expectation.