another question for you knowledgeable peeps...

In Storey's Guide to Raising Chickens by Gail Damerow she lists some causes:

certain drugs - especially coccidiostats
Viral diseases that affect the reproductive system
stress - overcrowded nests, rough handling loud noises and anything that makes a hen nervous or fearful = an inexplicable lightening shows something is bothering your hen
Eggs of a brown egg layer lighten as the hen ages.


I've heard for Marans that the color lightens during the laying cycle. Chickens lay a "clutch" and the eggs at the start are darker than those at the end. Then the chicken will pause, and start another clutch of eggs.

 

My brown eggs lighten throughout the year. Come spring when the girls start back at laying, the eggs are dark and the color fades over the summer. I look at as if their color sprayer is just getting low!

 

I have 5 hens all from the same clutch and none of them lay the same color eggs. They range from beige with small white spots to a rich creamy coffee color.

 

The longer the hen lays without molting, the lighter the brown egg shells become. After they molt, the egg shell color comes back. It's amazing how pretty those egg shells are after a molt. You'll notice the same thing if a hen goes broody and raises chicks. When she starts back laying, the egg shell color is nice.