Modern egg production provides consumers with several choices in fresh eggs. The most easily observed choices are egg sizes and brown or white egg shells. An egg shell's color is determined by the breed of hen that lays it, with variances of color within a breed. The color of the shell is simply the color of the shell, so base your choice on other factors when you purchase eggs.
If you want brown eggs for aesthetic reasons, buy them. Some people prefer brown eggs because they somehow equate shell color with healthy eggs, but a healthy hen will lay a healthy egg, so don't assume that brown eggs are better for you. Whether you buy from the supermarket or straight from a farmer, you'll find brown eggs range from very dark-shelled to light tan, sometimes with speckles. Brown-egg breeds are often selected for organic and sustainable farms because their hardiness suits them to free-range environments, so look for these certifications on the carton if these issues are important to you.
The size of an egg, no matter what color the shell, is primarily determined by the age of the hen and the breed. Egg size is graded by the weight of the egg. Young pullets of any breed in their first-year of production lay slightly smaller eggs; the egg size increases as the pullets mature. Some breeds are naturally heavier and produce larger eggs than other breeds, such as Wyandottes and Plymouth Rocks. Brown eggs are typically large, extra-large or jumbo simply because the breed is a larger bird. Brown eggs may be more expensive because the larger breeds of hens need more feed and more space per bird, which raises production costs.
Taste and Cooking
The taste of an egg is influenced by the hen's diet. Many people think they can taste a difference between white- and brown-shelled eggs, but the shell color does not influence this. Many cooks prefer brown eggs simply because brown shell bits are easier to see to remove from a cracked egg in a bowl or from a hard-boiled egg.
No nutritional differences exist between differently colored eggs. The nutritional composition of eggs is affected by the hen's diet. A new type of egg labeled as "enriched" or rich in omega-3 is available in both brown and white shells. Hens that lay these eggs eat a diet supplemented with natural sources of omega-3, such as flaxseed and fish oil, and their improved nutrition carries over into their eggs. According to a study published in "The American Journal of Clinical Nutrition," enriched eggs offer consumers benefits from omega-3 fatty acids -- eicosapentaenoic acid, or EPA, and docosahexaenoic acid, or DHA. When metabolized, EPA and DHA positively affected blood triglyceride levels and the levels of HDL, the "good" cholesterol, in the study group participants.