My brown egg laying hens have laid their eggs on the ground outside, and from the roost (onto sand also onto shavings) on three separate occasions. Those eggs have had a strange white/grey color to them. When removed from refrigeration they revert to their normal color, but when returned to the fridge they change back. What causes this? This egg was just removed from the regrigerator. The darkish end was in the egg carton. I haven't been able to find any info on this and would like to understand the cause. Thank you!