Welcome to BYC! Great to have you here!
I get eggs like that sometimes. I don't know who's doing it nor what causes it, but I don't think it's anything to worry about. Mine are most likely pullet variations. Someone else may have more knowledge about this.
As for the brown color, it gets added after the shell is formed. The color of eggs will lighten up through the laying season as the hen uses up her pigment stores. I expect this is related to aging. Again, I'm not an expert, but I wouldn't worry if it were my hens.