My Buffs' eggs are turning from brown to almost white??

[sylviabobby]

My Buff hen's eggs are turning from brown to almost white. This happened over a 2 week period. I have 13 laying hens and get an eggs from each almost daily. What would make them start getting lighter and lighter in color?

 

[Den in Penn]

Eggs laid latter in the cycle tend to get lighter then the first eggs. The glands producing the pigment get tired or the raw materials get scarcer.