Chicken eggshells can vary in color, which is determined by the breed. American buyers (except in New England) prefer white-shelled eggs. The most common commercial chicken is a White Leghorn. These are prolific egg layers (easily laying more than 300 eggs a year). They mature fast, are not very large, and lay white eggs.
The next-most-common choice for commercial egg laying is a hybrid Rhode Island Red (crossed with a White Leghorn) which lays a great number of buff-brown eggs. They are also quick-growing, rather small birds.
The goofy thing about chickens and egg color is that the ear lobe color of a chicken indicates
the color of the egg. Breeds with white feathers and ear lobes, such as White Leghorns, lay white eggs. Those with red feathers or ear lobes, such as the Rhode Island Red, New Hampshire, Orpington, and Plymouth Rock varieties, lay brown eggs. But by no means is that the limit of the color choices when it comes to chicken eggs. You can find breeds that lay a snow-white egg, whereas others lay deep-chocolate-brown or light-brown eggs or eggs in shades of pink, green, or blue. The variety is amazing.
In case anyone ever asks: The pigment is deposited on the egg as it moves through the oviduct.
Egg sizes differ by breeds as well. Although an older chicken always will lay a larger egg, “larger” is relative. There are bantam chickens (about half the size of a standard chicken) that produce a dainty small egg, often smaller than the U.S. Department of Agriculture (USDA) peewee size. There are also individual chickens that lay much smaller, or much larger, eggs than what is standard for their breed.
There are hundreds of chicken breeds, each with individual features and egg laying abilities. Some people insist that you can taste the difference between eggs from different breeds. From my experience, there are certain chicken breeds that seem to consistently lay eggs with larger yolks.