Fascinating! I found this article that shows a double shelled egg and in the photo example, it does look like the color is slightly different.
"EGG WITHIN AN EGG:
An egg within an egg, or a double shelled egg appears when an egg that is nearly ready to be laid reverses direction and gets a new layer of albumen covered by a second shell. Sometimes the reversed egg joins up with the next egg and the two are encased together within a new shell. Double shelled eggs are so rare that no one knows exactly why or how they happen. The photo below was provided by one of our website visitors, Michelle Byerly, of Jasper, Texas. The bowl is a standard single serving cereal bowl. The egg was laid either by a Buff Orpington or a Black Australorp in early 2004. The egg found inside the other had no yolk (fart egg)."
https://www.poultryhelp.com/oddeggs.html