What is the difference between white and brown eggs?
The Egg Nutrition Center's FAQ page has an entry on this very topic. Basically, the color of the egg does not affect the egg's flavor, nutritional value, etc. It simply depends on the particular breed of chicken that lays the egg -- white eggs from white hens, brown eggs from brown hens.

It's also worth noting, as the ENC points out: 


  Generally, brown hens are larger and
  require more feed and therefore their
  eggs may be slightly higher priced.