Yes My partridge penedesenca that was just offed by a hawk was laying a nice dark brown egg.The Feathersite's list of breeds usually lists the breed clubs and some breeders.
Marans, Penedesenca, Empordanesa, Welsummer, Barnevelder and some Langshans lay dark eggs.
I just got some real nice empordanesa eggs that a really dark chocolate egg.