I think you'll find that hatchery Marans are going to turn out like other hatchery birds. They are not selectively bred, so although they are genetically Marans, most will never lay very dark eggs like those from breeders.
We had some hatchery Marans, and a few layed some dark eggs, I'd say we never got above a 5 on the egg chart.
Go to this link for the Marans eggs chart:
http://www.maransofamericaclub.com/marans_eggs_60.html
These birds have since been rehomed, and we acquired better birds.
We now have some from a breeder here in NY, and they came out of very dark eggs. They weren't cheap, but it will be worth it. Can't wait to see what happens.
But, I am truly sorry you are disappointed. It takes a while to figure all this out...
It is disappointing when you buy something thinking it will be what you want it to be, or do what you want it do, and it isn't/doesn't!
The will start out darker, then lighten up. I would say the first few eggs will be a good indicator of the darkest they will be. They will lighten up...