Last Updated: 8/5/2026
Walk down the egg aisle, and you may see eggs with white, brown, blue, green, or even speckled shells. It’s natural to wonder what determines the color of an eggshell and whether those colors mean anything about nutrition, quality, or freshness.
Eggshell color is one of nature’s most visible examples of biological variation. While shell colors can look dramatically different, the science behind them comes down to genetics and a small number of pigments working during a specific stage of egg development.
We believe transparency helps consumers make informed choices. Learning about eggshell color is one more way to appreciate the remarkable biology behind every egg.
How Eggshell Color Is Formed
Eggshell color is primarily determined by a hen’s genetics and the pigments deposited during egg formation. In scientific terms, eggshell color is the visible hue created when a hen deposits pigments onto the calcium-carbonate shell as the egg moves through her oviduct.
The process of forming an egg typically takes a little more than 24 hours. During that time, the yolk, egg white, membranes, shell, and shell color are added in stages as the egg moves through the hen’s reproductive tract. At its early stage, the shell begins as white calcium carbonate, and then the color is added.[1]
The Two Main Pigments Behind Eggshell Colors
Most eggshell colors can be explained by two primary pigments: protoporphyrin and biliverdin. The presence, timing, and combination of these pigments determine whether an egg appears white, brown, blue, green, or olive-colored.[2]
Many bird eggshell color differences can be explained largely by these two pigments, either working alone or together. Some birds produce little or none of either pigment, resulting in white eggs.[3]
What Is Protoporphyrin?
Protoporphyrin is a reddish-brown pigment associated with hemoglobin metabolism that is deposited late in shell formation, primarily coating the outer shell surface. It is responsible for brown and reddish-brown eggshell colors.[4] [5]
Because protoporphyrin is deposited late in the egg-forming process, it usually does not penetrate deeply into the shell. When you crack a brown egg, the inside of the shell is often white.
What Is Biliverdin?
Biliverdin is a blue-green pigment that becomes incorporated throughout the shell matrix during shell formation. This pigment produces blue and green eggshell colors and often colors the shell both inside and out.[6] [7] [8]
Unlike protoporphyrin, biliverdin can permeate the shell structure. This is why blue eggs typically remain blue on the interior surface after cracking.
Green eggs are often produced when brown pigment overlays a shell that already contains biliverdin. This layered effect commonly occurs in crosses between blue-egg and brown-egg breeds.
Genetic Factors Influencing Egg Color
A hen’s breed and genetics largely determine the type and intensity of eggshell pigment she deposits. Different breeds have inherited traits that influence which pigments are produced and how much pigment is deposited during shell formation.
For example, White Leghorns are famous for laying white eggs, while Plymouth Rocks and Rhode Island Reds are well known for producing brown eggs. Ameraucanas, Araucanas, and Cream Legbars are among the best-known blue egg breeds.[9]
Common Breeds and Egg Colors
| Breed | Typical Egg Color |
|---|---|
| White Leghorn | White |
| Plymouth Rock | Brown |
| Rhode Island Red | Brown |
| Ameraucana | Blue |
| Araucana | Blue/blue-green |
| Cream Legbar | Blue |
| Dongxiang | Blue/blue-green |
| Lushi | Blue/blue-green |
| Olive Egger (cross) | Green/olive |
We partner with family farms that may manage flocks with different genetic backgrounds. Learn more about our hens and how our farmers raise them with Certified Humane® care.
Environmental and Physiological Influences on Shell Color
Genetics establishes the baseline eggshell color, while environmental and physiological factors can influence shade, intensity, and uniformity. Even hens from the same breed can produce eggs with slight color differences. These variations are usually normal and reflect natural biological processes rather than quality concerns.[10] [11] [12]
Factors That Can Influence Eggshell Shade
- Age: Older hens often lay larger eggs, which can appear lighter because pigment is distributed across a larger surface area.
- Diet and mineral status: Nutritional deficiencies may affect shell formation and pigment intensity.
- Stress: Stress can influence pigment deposition and timing.
- Oviduct timing: Changes in how long an egg remains in the reproductive tract can affect shell appearance.
- Individual variation: Pigment production naturally varies among individual hens.
What Eggshell Color Means for Nutrition and Quality
Eggshell color is not an indicator of an egg’s internal quality, taste, freshness, or nutritional value. However, there are some factors that do influence nutrition and freshness.[13]
Factors That Influence Egg Quality
- The hen’s diet and nutrient intake.
- The hen’s living conditions and welfare standards.
- Freshness, storage, and handling practices.
- Farming and animal care practices.
For domestic chickens, speckles and spots are usually the result of extra pigment or calcium deposited during shell formation. These markings are harmless and do not affect safety, freshness, or nutritional value.[12] [14]
When choosing eggs, look beyond eggshell color. All Pete & Gerry’s eggs (Organic Pasture Raised, Pasture Raised, and Organic Free Range) come from U.S. family farms that follow Certified Humane® standards. We’re proud to partner with family farms that share our commitment to humane care, responsible farming practices, and transparency.
More Than Color: Understanding the Story Behind Every Egg
Eggshell color is one of the most visible differences among eggs, but it’s also one of the least important when it comes to nutrition and quality. What determines the color of an eggshell is the interaction between genetics and pigments deposited during shell formation. These pigments create the beautiful variety of white, brown, blue, green, and olive eggs that consumers enjoy today.
Frequently Asked Questions About Eggshell Color
Q: Why are some eggs white and others brown?
Eggshell color is primarily determined by a hen’s genetics and the pigments deposited during egg formation. Different breeds deposit different pigments during shell formation. For example, White Leghorn hens typically lay white eggs, while Plymouth Rocks and Rhode Island Reds commonly lay brown eggs.[1] [2] [3] [9]
Q: Does egg color affect taste or nutrition?
No. Eggshell color does not affect taste, nutritional value, freshness, or internal quality. Nutrition is influenced more by the hen’s diet and management than by shell color.
Q: What makes blue or green eggshells?
Blue eggs get their color from biliverdin, which permeates the shell. Green or olive eggs often occur when brown pigment overlays a shell that already contains biliverdin.[6] [7] [8]
Q: What makes eggshells brown?
Brown eggshell color comes from protoporphyrin, which is deposited on the shell’s surface late in the hen’s egg-laying process. Hens with red or brown feathers typically lay brown eggs.
Q: Are brown eggs healthier than white eggs?
No. Brown eggs are not inherently more nutritious than white eggs.[13] The nutritional profile depends primarily on the hen’s diet and management, not shell color.[9]
Q: Why do some eggs have speckles or spots?
Speckles are usually caused by extra pigment deposited during shell formation. They are a natural variation and do not indicate a quality or safety issue.[12] [14]
Q: Can a hen lay different colored eggs?
A hen generally lays the same base shell color throughout her life because shell color is genetically determined. Small shade variations may occur due to age, nutrition, stress, or health factors.[13]
Q: Why are some brown eggs darker than others?
Brown shell intensity varies due to genetics, age, stress, and individual differences in pigment deposition. Many hens lay darker eggs earlier in their laying cycle, with color becoming lighter over time.[11] [12] [13]
Q: Why are eggshells colored on the outside but white inside?
Brown eggs are usually colored by protoporphyrin, which is deposited primarily on the shell surface late in the egg-forming process. Blue eggs differ because biliverdin permeates the shell matrix and colors the shell throughout.[4] [5] [6] [7] [8]
Q: Are colored eggs safe to eat?
Yes. Eggshell color does not affect food safety. Proper refrigeration, handling, and cooking practices are important regardless of shell color.
References
- Ohio State University Extension. The Making of an Egg.
- Huang, H., et al. (2023). The pigments in eggshell with different colour and the pigment regulatory gene expression in corresponding chicken’s shell gland. Animal.
- Emily Teel for Serious Eats. Brown, White, or Blue Eggs—What Matters for Taste (and What You’re Really Paying For).
- Samiullah, S., et al. (2015). Eggshell Color in Brown-Egg Laying Hens: A Review. Poultry Science.
- Liu, M., et al. (2021). Mechanisms Associated with the Depigmentation of Brown Eggshells: A Review. Poultry Science.
- Sparks, N. (2011). Eggshell Pigments: From Formation to Deposition. World’s Poultry Science Journal.
- Wang, H., et al. (2025). Improved Shell Color Index for Chicken Eggs with Blue-green Shells Based on Machine Learning Analysis. Foods.
- Zhao, R., et al. (2007). A study on eggshell pigmentation: biliverdin in blue-shelled chickens. Poultry Science.
- Hanna Ingold for The Hen House Collection. Chicken Egg Colors: A Complete Guide.
- Drabik, K., et al. (2021). The Variability of Quality Traits of Table Eggs and Eggshell Mineral Composition Depending on Hens’ Breed and Eggshell Color.
- Benavides-Reyes, C., et al. (2021). Research Note: Changes in eggshell quality and microstructure related to hen age during a production cycle. Poultry Science.
- Paul Schattenberg for Texas A&M AgriLife Today. Why Are Eggs Different Colors?
- Healthline. Brown vs. White Eggs—Is There a Difference?
- University of Georgia Cooperative Extension. A Dozen Egg Abnormalities: How They Affect Egg Quality.
