As Americans down an average of nearly 300 eggs a year, you’ve likely cracked open an egg to see a yolk slightly different than what you’re used to, whether a bright orange or pale yellow yolk.

Seuss books. Though you probably won’t encounter green eggs and ham anytime soon (but it’s possible), yolk colours can vary from the palest yellow to reddish brown. What affects the colour of ...

A small creature with a “yolk-yellow” underside sat on a mountain in southwestern China and breathed in the thin air. Something about the animal caught the attention of nearby scientists.