Brown, Green, Blue, White: Chicken Egg Color – The Real Story

A dozen eggs bought at the supermarket are all the same, smooth and identical in shape and color; any variation that does occur is sorted out by machines and by workers in the factory and don’t end up in cartons. In contrast, the eggs from our own backyard hens are a varied lot, which is no surprise as our chickens, unlike the ones in the commercial production facilities, don’t look alike. The eggs in our cartons are as unique as the birds that lay them.

On the most basic level, breed determines the color of the egg. You can try to select your backyard hens with an eye to what your egg basket will look like, but it doesn’t always go as planned. But, each hen has their own genetic makeup, and don’t always follow the rules. I got a Welsummer because they are known to lay chocolate-colored eggs. My Welsummer, Jasper, lays beige eggs. It’s my Rhode Island Red that lays deeply brown eggs with speckles.

How the egg becomes colorful is fascinating and complicated. It takes about 26 hours for an egg to go from the ovary until it is laid. First the yolk is encircled with whites and membranes. Then this jelly-like mass goes into the shell gland, where it will spend about 20 hours while the shell is formed.

The shell is made up almost entirely of calcium carbonate, which is a white mineral. White eggs are white, through and through. But, during the last four to six hours in the shell gland, a brown egg-laying hen adds pigment to the mix. This is why the insides of brown eggs are white – the egg starts out white, and gradually becomes more colorful. In the last 90 minutes, the rate of shell formation slows, and the cuticle, a viscous, protein-rich fluid (also called the bloom) is added. (The cuticle is the first line of protection against bacterial infection in the egg.) This is also when the hen secretes most of the pigments into the shell.

A lot can interfere with this process. If a hen is stressed, she’ll release a hormone that ceases the cuticle formation and so her shell color will be pale. Some viral diseases can decrease shell color. Certain medications can impact pigmentation. The size of the egg can affect color, too. The hen is genetically programmed to make a certain amount of pigment. If she lays a very large egg, there’s less pigment to go around. As a hen ages she becomes less able to synthesize the pigment and so her eggs will lighten over time.

As the egg moves down the passageway it rotates. If it goes slowly, the egg will have dark speckles. A notch up in speed and there will be streaks. Sometimes it will look chalky. Sometimes, half of the egg is darker than the other, and it appears to have been dipped in dye. This is because the egg moves through the passage round side first. That end, pushing through, has more contact with the papillae that excrete the pigment, and thus it’s laid on with more pressure.

This process is even more complicated for blue egg layers. Blue pigment is a different chemical than the brown. It’s scientific name is biliverdin, and it is derived from hemoglobin (a component of blood.) It is metabolically costly for the hens to create. A recent study of Blue Footed Boobies show that the blue color will become even more pronounced with an increase in carotenoids in the birds’ diet. (I’d like to see a teenager do a science fair project with their Araucanas to see if they can replicate this work with chickens!) Biliverdin is added to the calcium carbonate earlier in the shell-making process, and so the eggs appear blue all the way through. Chickens that lay greenish, gray, or dusky blue eggs produce both biliverdin and brown egg pigments. The brown overlays the blue.

It’s been said that the brown pigment can be removed. When an egg is first laid it is still damp. In the short window of time while it dries, the cuticle can be rubbed off, and so much, but not all, of the brown pigment along with it. Certain breeds (and some individual hens) deposit pigments in the last few minutes of shell-making, and so, it seems as if it’s just dye to be wiped off. But, scrubbing removes not just color, but also the all-important bloom and calcium carbonate. Because I’ve heard so much about the permanence/impermanence of shell color I did some experimenting. I wiped, I used abrasive baking soda, I used a stiff brush. Some eggs lost some pigment. Some lost none. As you can see, none became white.

But, I do rather like the egg that looks like it has a bald pate. Perhaps I can start a new trend in Easter egg decorating?


  1. Very informative article. Thanks and keep it coming I learn so much from all my eggs friends!

  2. Very interesting! I had no idea about rotation, last-minute pigmentation and more. Thanks for the information. Chickens are even more wonderful and amazing than I already knew.

  3. biliverdin and bilirubin (the other breakdown product of haemoglobin) are also the things that make a bruise go through that lovely technicolour extravaganza as it fades! You could scrub off letters in the pigment to make personalised eggs…

    • For a long time scientists though that biliverdin had no intrinsic value, but now they think it’s a powerful antioxidant. Perhaps helpful around those bruises?

  4. This is so interesting Terry, thank you for sharing your research. As an owner of Araucanas and AraucanaxCrestedCreamLegbar hybrids, the variations in the blue/blue-green colour are fascinating.


  5. As kids, my mother would have to buy us white eggs from the store because we couldn’t properly color our farm eggs :)

  6. I like the Friar egg, too. Definitely has potential. Thanks for the info.

  7. Wow. This was such an interesting and informative post. I think I’ll have to read it several times to digest everything. I loved it, Terry. Thank you!

  8. Lately I listened to a radio interview with a Jewish man. He explained that orthodox Jews prefer white eggs, because white eggs do not contain blood as often as brownish eggs. I wonder if this is true, and, if so, what the relation is between the color of the egg shell and the presence of a tiny bit of blood inside.
    Have you ever heard about this?

    • Not one bit of truth to it. It might be that many years ago a white egg supplier sold infertile eggs, and hence no chance of a developing embryo, and the Jewish community got into the habit of buying white eggs. A century later, they can’t remember why they buy white eggs, but they still do. The egg spot doesn’t even have to do with fertile eggs – it is caused when the yolk releases from the ovary. Has nothing to do with egg shell color.

      • I have heard/read, though, that certain breeds are more prone to lay eggs with blood spots or meat spots (something that occurs even in unfertilized eggs.) I became aware of this because my Cuckoo Marans’ eggs always seemed to have a blood speck (I do not have a rooster and they are 100% infertile). Upon investigation, I’ve found information that this breed, and other brown egg layers, do tend to have a higher incidence of such imperfections than others. Granted, genetics alone aren’t the only cause of blood spots or meat spots…
        But because commercial eggs (predominantly white, for years), as you pointed out, are subject to rigorous sorting and grading–and because white eggs are so much easier to candle, this too probably lends to white eggs having a lower likelihood of any such “imperfections”.
        Just a thought.
        All of my hens are brown layers, and I wouldn’t have it any other way. All of the different hues and shapes make for such a beautiful egg basket, I’m thrilled to pieces every time I find a warm one in the nest box!

        • Actually, your comment about candling makes a lot of sense! It is easier to see blood spots in white eggs. BTW, here on the east coast of the USA there’s the thinking that brown eggs are fresher. This stems from about 75 years ago when New England farmers raised only brown egg-laying hens and in the south they had white leghorns. So, if you lived in Boston, you knew that white egg was older and had traveled! It’s no longer true and white and brown eggs come from all over, and of course there’s rapid transportation now. But, people remembered “brown eggs are fresher” and many still think it!

          • My Israeli friend Lea always told me that the white eggs were easier to candle too, and her grandmother only had white egg laying breeds on their farm outside Tel Aviv for just that reason. Even after 25 years living in London white eggs still remind her of home!

          • I remember that tune on TV…”Brown eggs are local eggs, and local eggs are fresh!”

            • The power of advertising! Did you know that Perdue, to distinguish their chickens, fed them an extract from chrysanthemums in order to turn the skin yellow. Then they marketed the yellow-skinned chicken as fresh chicken. Now most consumers think that yellow-skinned chicken is the best.

              • I’ve been doing some reading on this. The original dietary rules were developed when all flocks had roosters and the ban against blood spots was done with the thought that there was a developing embryo there. Some modern rabbis recognize that blood spots are a different category of blood, and that the egg can still be consumed if the egg spot is discarded.

              • Yet more info from my foreign friends – great pal Nyreen grows marigolds in Zambia commercially to add to chicken feed as a yolk colourant! Very profitable apparently and a pleasant crop to work in.
                We get bloodspots here when the Tornado jets practise low over Kent….

  9. Terry this last week one of my red stars laid an egg that weighed 3.9 then a couple of days later one that weighted in at 2.6. I am still showing the eggs off large one has a slight crack around middle so will discard after show and tell. ? I have been getting blood spots and on occasion a dark spot that looks like an old apple seed when I crack the eggs open any way to prevent this? I give most of my eggs away and how do I warm people that are use to buying to expect blood spots

    • I could do a post just about blood spots! But the quick answer is that the yolk is formed in the ovary, which immeshed in capillaries. When a yolk is released a spot of blood might burst off, and that’s what’s on the yolk. There is a genetic component – brown egg layers are more prone to this. But, it’s also linked to fear and stress, so keep your hens calm :) The consumers of your eggs should be told that it’s perfectly natural and all they have to do is discard that little dark lump.

  10. We are blessed to give a dozen eggs each week to a widow friend with 3 children, so yesterday they all came to see my “girls”. They enjoyed holding my Buff Gabby, and one of the Bard Rocks. So yesterday, since this family is fascinated with the brown speckled eggs, and the 10 yr. old girl has taken the eggs to school for “show & tell”, I gave her a printed copy of your Feb. 10 blog on “…The Real Story”, how eggs are made. So thank you Terry for all the great information that I can pass on to others.

  11. Interesting stuff!

    Anybody know how the cuticle/bloom affects dyeing eggs? I would assume that commercial eggs have been mechanically washed, removing some of the bloom.
    Last few times I dyed Easter eggs, I dyed brown store-bought eggs, and I enjoyed the duller, more natural looking tones.

    BTW- a fun thing to do with eggs: put an egg in a jar and fill it with white vinegar. After a few days, the shell dissolves away. I am not bold enough to try eating such an egg, but a shell-less hard-boiled egg would be pretty amusing.