There are several breeds of chickens that lay dark brown eggs, including:
1. Marans: This breed of chicken is known for its dark brown eggs, often classified as chocolate brown. The egg color is a result of a pigment called protoporphyrin.
2. Welsummer: This breed is known for laying eggs with a deep, reddish-brown color that sometimes has speckles on the surface.
3. Barnevelder: This breed is known for laying dark brown eggs with a slight sheen on the surface.
4. Black Copper Marans: This particular variety of Marans is known for laying the darkest of the dark brown eggs.
Note that egg color can vary among individual chickens of the same breed, and factors such as diet, age, and environment can also affect the color of the eggs.