Do eggshells let flavours pass through during boiling?
Yes, they will taste different. Egg shells are porous in order to provide oxygen to the developing chick. While the egg is still uncooked, it will take on the tastes of outside ingredients fairly easily. As it cooks, the albumin coagulates and forms chains that prevent moisture and vapor exchange, so it becomes resistant to absorbing outside ingredients. As a result, your egg will pick up more curry taste if it is boiled from raw in the curry sauce than if you boil an already-cooked egg in the sauce.