Variation in the color of the yolk has nothing to do with freshness and everything to do with the diet of the chicken.

Natural yellow pigments, going by the catchy name of xanthophylls, are responsible for the color of the egg yolk. Xanthophylls are not produced by animals, though, so they get to the hens by way of the dinner plate, and are then deposited in the yolks.

If hens are fortunate enough to be fed mashes containing yellow corn or alfalfa meal, they produce eggs with medium-yellow yolks. If their feeds are based on wheat or barley, they produce lighter-colored yolks. To get orange yolks — which to many people imply farm eggs or free-range eggs or fresh eggs or tastier eggs or "healthier" eggs — marigold petals or other naturally orange plant matter may be mixed in with light-colored feeds. In this country, the use of artificial color additives in hens' diets is not allowed.

It is even possible to produce nearly colorless egg yolks by feeding hens white cornmeal or other pale grains. Needless to say, no one but nearly insane molecular-gastronomy-obsessed freak chefs would buy them. But some nearly insane molecular-gastronomy-obsessed freak chef would probably turn clear yolks into a vacuum-packed, sun-dried, tisane-scented crispy biscuit with marigold-petal foam, offer it on the menu for $165, and wind up on the cover of Bon Appétit magazine as the year's most creative young chef. Or worse, as this year's Top Chef!

Outside the chicken pen, xanthophylls are seen when the leaves turn yellow and orange in the fall, once the bossy green chlorophyll ceases to dominate the leaves.