I just had one of my Favaerolle hens lay a snow white egg yesterday, and my first thought was, "OK, who snuck a white egg in there...?"
Here's how I see it. The yolk goes down the bird's egglaying tract, and then the albumum is added onto the yolk, and next comes the membrane, then the shell is added on. The last step is like a spray paint job, the eggshell color is added to the white shell (or maybe the eggshell color is already part of the shell that was added on? Oh well. I've always visualized the egg laying process as being like a car running though a car wash... you know, first the water, then the soap, then a scrub, etc. So I'm thinking my hen's egg must have come out white because her paint spray is jammed up or not working.
Ok, I know that's not scientific, but that's how I visualize it all. I should go online and search out the steps for an egg to come out, from yolk (with or without fertillized ova) to ready to hit the nest.
Any other theories out there?