Could you post a picture of your Marans? I've heard about people being disappointed with a Marans laying medium brown eggs. But if they're tan, it makes me wonder if maybe your bird isn't a Marans after all?
She is a Black Copper Marans. She started laying maybe 2 1/2 weeks ago, and her eggs are the color of all of my other brown egg layers. This isn't the greatest picture, but it is the only one I could get of her standing still.
I'm still learning about the BCM's... hopefully somebody with more knowledge will be able to help. What color are her legs? They should be black... and she does have a lot of extra 'copper' down her chest for a BCM... perhaps she has something else mixed in with her. She is a beautiful pullet tho! You might try posting her pic in the BCM's thread? Maybe they can tell you more.
I know nothing about Marans, but a quick Google search reveals more than a few sites that say they should all have "white or horn beaks" and white feet/legs, as well as bright red or orange eyes. The photo you posted isn't that clear, but the beak looks quite dark, as do the eyes.
I am curious about this as well. I am getting Cuckoo Marans in February from McMurray Hatchery and I would like to know if anyone knows if they have a good line for dark brown eggs? Also- does anyone know if there is something specific that I can feed them to make their eggs darker? Thanks!