I had this problem and put golf balls in the nests: problem solved. I can imagine that a few pecks at a golf ball is a powerful disincentive for egg eating.
We also feed them kitchen scraps. I read somewhere that they can get bored, leading to eating their eggs.
This strikes me as odd...
I just collected the eggs from our 11 chickens. They are various breeds and we get both brown and white eggs.
Tonight I noticed that a few of the eggs had green splotches on them. Just one or two small irregularly shaped spots, not taking much space on the shell, and on both white and brown...