鸡蛋有红皮、白皮、绿皮，有什么区别？

Peruse the egg section of a grocery store or farmers market, and you'll notice cartons of eggs separated into white and brown, sometimes even green or blue eggs. But once they arrive scrambled on a plate, perhaps, or baked into a cake, it's tough to tell the difference. In fact, what is the difference between eggs with shells of different colors?
去超市或农产品市场仔细观察成箱的鸡蛋，你可能会注意到鸡蛋既有白的，也有褐色的，有时候甚至是绿色或蓝色的。可是变成炒蛋或蛋糕之后，又基本看不出区别了。那么，这些鸡蛋除了蛋壳颜色不一样，还有什么不同呢？

This isn't a flour or rice situation. Brown eggs are not more "natural," and white eggs have not been decolored with bleach. Both varieties occur completely naturally, as do bluish-green chicken eggs. But really, all chicken eggs are the same on the inside. So what causes different egg colors among the same type of bird?
这跟面粉或大米不一样。褐色的鸡蛋不一定更“纯天然”，而白色鸡蛋也不是被漂白了。相反，它们生来就是那样的，包括蓝绿色的鸡蛋也是。但不管蛋壳颜色如何，它们的内在实际上都是一样的。那为什么这些鸡蛋都是母鸡生的，“肤色”却各有不同呢？

Dr. Justin Fowler, a professor in the University of Georgia's poultry science department, shines a light on things. "The different colors, or the presence of spots or speckling, come down to the genetics of the bird," he says.
乔治亚大学家禽学系的贾斯汀·福勒教授对此作出了阐释：“鸡蛋颜色不同，或者有些带有斑点，是母鸡基因不同导致的。”

"Leghorn chickens (which make up most of the commercial egg industry in the US) lay white eggs, while Orphingtons or Plymouth Rocks will lay brown eggs," explains Fowler. "The Ameraucana breed has a pigment that is able to permeate the whole egg shell and make blue-colored eggs that are colored on both the inside and outside of the shell."
“来亨鸡是美国最主要的商品蛋鸡，它们会下白色的蛋；奥尔平顿鸡和洛克鸡下的蛋则是褐色的；而阿美饶卡纳鸡身上会产生一种色素，能够渗透到整个蛋壳里，让蛋壳里里外外都变成蓝色。”

Want to know whether a specific chicken will pop out a white egg or a colored egg? Examine the chicken's earlobe. (Surprise, birds have earlobes!) "Breeds with white earlobes will typically be those that do not put extra pigment on the egg shell before laying," says Fowler. And more often than not, chickens with lighter earlobes tend to have white feathers, and thus white eggs, while those with colored feathers and earlobes tend to produce colored eggs.
想要知道某只鸡下什么颜色的蛋，可以看看它的耳垂是什么颜色（没错，人家鸡也是有耳垂的！）福勒说道，“白色耳垂的鸡产蛋时通常不会分泌色素，所以下的蛋通常是白色的。”一般来说，耳垂颜色较浅的鸡羽毛都是白色的，下的蛋也是白色的，而羽毛和耳垂有色的鸡则会下有色的蛋。

Where does this color come from? Here's where understanding how an egg comes to be is important. Chicken yolks, or ova, form in the chicken's ovaries. A fully formed ovum will leave the ovary and be deposited into the oviduct. This part of the chicken's reproductive system has five distinct sequential segments which the yolk passes through on its way to the outside world, but it's the fourth one — the shell gland — that affects the color of the egg. This is where the shell forms around the ovum.
这些颜色是怎么来的？这就要从鸡蛋的形成过程说起了。母鸡的卵巢里会首先孕育出蛋黄（也就是卵子）。成熟的卵子会离开卵巢来到输卵管。在输卵管中，卵子会按顺序经过五个部分，然后才到达体外；其中第四个部分是卵壳腺，蛋壳就是在这里形成的，这个部分影响了鸡蛋的颜色。

"The shell of all chicken eggs are made of calcium carbonate, a crystal that is white in color," says Fowler. "So all eggs are, at least at the start, white. Any that we then see that are other colors have had a pigment deposited on them as they were moving through the oviduct, after the white egg shell had been deposited. You can see this if you open up a brown egg and look at the inside of the shell, it'll be white."
福勒称，“所有蛋壳都是由碳酸钙组成的，碳酸钙是一种白色晶体。所以所有鸡蛋至少最初都是白色的。有色的蛋壳都是在经过输卵管时被染了色。不信你可以敲开一个褐色的鸡蛋，看看蛋壳内部的颜色，那一定是白色的。”

Two pigments are responsible for the spectrum of chicken egg color. Shades of greens and blues are caused by the pigment biliverdin, while protoporphyrin is responsible for reddish-brown hues.
决定鸡蛋颜色的主要有两种色素。胆绿素会让鸡蛋变成蓝色或绿色，而原卟啉则会把鸡蛋染成红褐色。

The same egg-coloring process holds true for all birds with colorful eggs. American robin (Turdus migratorius) eggs, for instance, are famously blue. The pear-shaped eggs of a common murre (Uria aalge) can sport a blue hue, be speckled or feature brown streaks.
其它鸟类的蛋壳颜色也是一样的道理。例如，众所周知，美洲知更鸟下的蛋就是蓝色的，而崖海鸦的梨形蛋不仅是蓝色的，通常还带有斑点或褐色条纹。

****小知识****

Should chicken eggs be kept refrigerated or at room temperature? It depends on whether you live in a country (Australia, Japan and the United States, for instance) that requires eggs produced for commercial sale be washed. This process protects against salmonella, but also removes a waxy shell coating that naturally defends eggs against microorganisms, thereby necessitating refrigeration.
鸡蛋应该放冰箱里还是常温储存？这取决于你生活在哪个国家。澳大利亚、日本和美国等一些国家要求用于销售的鸡蛋必须经过清洗。清洗程序能够清除沙门氏菌，但同时也洗去了蛋壳上防御微生物的蜡状保护层，所以需要放冰箱里面。

至于咱们国内的鸡蛋，因为不清洗外壳，所以常温存放即可。

如果你在敲开鸡蛋后看见有血丝或黑色褐色的小点，不用担心，和蛋壳颜色一样，这是输卵管的“功劳”。“血斑”源自母鸡卵巢或输卵管的轻微出血。血液渗到卵黄上，被包裹到蛋中，就形成了“血斑蛋”。黑色褐色的斑点是母鸡输卵管脱落的上皮组织或其他异物，在形成蛋清的时候被包裹到鸡蛋中而形成，俗称“肉斑蛋”。

无论是红蛋、白蛋、绿蛋、褐蛋、血斑蛋、肉斑蛋，只要是新鲜鸡蛋，煮熟了都可以放心食用，营养价值也差不多。