One thing you’ll never see from a commercially produced egg is a “rooster spot” (aka meat spot). The scanning, washing, sorting, and weighing of eggs at commercial factories toss them aside for industrial cooking and baking (along with double yolks, and the extra small eggs). With a fresh chicken egg, and especially young chickens — laying their first year — you will run into it a lot. The old wives tale version of it was “that’s what the rooster contributed”. It’s not true. It’s just a slight malfunction in the egg creation process. The little blood spot doesn’t flavor the egg, nor make it unsafe to eat. Most people just take out the red spot with the tip of a knife. Some people just cook the egg, and ignore it. There are others that throw out the egg (an unnecessary reaction).
Most chickens will, eventually, stop throwing an off egg. But there are always mistakes that happen in the process. Some eggs will have double, triple, or more yolks (even if fertilized double chicks don’t develop, or survive). There are eggs with all egg white (often very small) called “wind eggs” or “fart eggs”. And, depending on the chicken’s diet, egg yolk color will vary. When chickens eat a great deal of green vegetable matter (they love to eat grass and weeds, and anything in your garden) and that will cause the egg yolks to have a brighter, deeper orange/yellow color.
Commercial eggs, by comparison, are often “colored” by use of annatto in the feed (it’s not disclosed as the FDA has certified it as “exempt from certification” and considered natural). Many people have sensitivities to annatto. People with nut and peanut allergies often react to it unfavorably. There has not been a widespread study about it. It’s just added to the chicken feed, colors the eggs, and that’s that. Buyer beware, I guess.
But, people with a sensitivity to chicken eggs, might want to make sure the allergic reaction isn’t to annatto, instead of eggs.