How old is she? From what I understand, the color of Marans eggs can actually lighten with age. However, if she hasn't been laying for very long, then it might be that her body is still getting used to egg laying.
I have a Silver Cuckoo Maran and my friend has a sister from the same batch. They are about1 1/2 years old. Mine lays normal brown eggs and hers lays deep chocolate colored eggs. Dont know what to tell you. Maybe its their diet.
My mother had Cuckoo Marans and they laid light regular brown eggs. In her research she had learned that only a few of these birds lay the chocolate eggs. There are other types of Marans and I don't know anything about their egg colors???
All Marans are french. The breed was named after the town/area where they were developed: Marans, France. My Cucko Marans lay eggs lighter in color than my RIR. My Black Copper Marans lay dark coppery brown eggs. They are about 1 shade lighter than the darkest egg on the Marans egg color chart.
Wow, this is all quite interesting to know. I had always thought that all color types of Marans laid the chocolate brown eggs. I just got a cuckoo Marans a couple of weeks ago, and the people I got her from told me she lays the dark brown eggs. Makes you wonder about some things.