@Frustration in Excelsis

Of course, chicken eggs also vary a lot in color — the white’s mostly due to battery chickens tending not to get the nutrients they need in their diet.

No, the difference in colour is simply a genetic trait that has only affects the colour of the shell. For a long time stores claimed brown eggs were “healthier” or “free range” as a marketing trick to sell the exact same egg for more money. The colour of the yolk, though, is an indicator of healthy vs battery.