Dark egg color is a fickle trait. A person can cross a female that produces dark brown egg color with a male that came from a dark brown egg and some F1 pullets can produce a normal brown egg. If you are going for a darker egg color- hatch plenty of eggs and then select for the best color. Read post 28 on the string.
https://www.backyardchickens.com/t/840867/clarifying-brown-egg-genetics/20#post_12619560
Read the following;
http://www.maranschickenclubusa.com/files/eggreview.pdf
Tim
Tim,
Thanks for the information.... very interesting and well written. It also answered a 2nd question I had about my EEs laying eggs that were blue all the way through.