Egg layers off schedule

Our hens are laying eggs in the afternoon. And, all four hens are the same kind of hen, brown feathers and kind of big gals. They just started laying and two lay blue eggs and two lay really dark brown eggs. Is this normal or is something wrong with their internal clocks and their egg shells being different? We eat the blue and the brown eggs but I was worried something might be messing with their eggs. I feed them the same diet and I would ask my neighbor who has white hens but I am slightly embarrassed being so ignorant about our hens that we actually rescued from a terrible situation.