To me they are good looking birds so far. Different lines mature at different rates. My Bev Davis line blue rooster has QUITE A BIT of white leakage in his sickle feathers. Maybe a quarter of his hard tail feathers show the fault, and you can see it from fifty feet away. My CBM from bayhorsebonne, Wade Gene/Ron Presley lines, has one or two tail feathers that moult out with varying degrees of white streaks in them, differs from moult to moult. I get some little white feather tips on the feet too. If I get a stark white flight feather, they are outta here. The white streaking at the base of feathers, I am working with at the moment, breeding, growing out, selecting the best stock I can. Breeding marans, you have to grow out a lot of birds and cull a lot to get anywhere. You learn to eat BEAUTIFUL roosters, tame, large, gorgeous heads, perfect combs, wonderful in the flock and around people... because you have to grow out so many to get a better one. Just the way it is. And you won't know for MONTHS if they are going to grow out of their mossiness, or develop too much copper on their chests, or get white streaks in a few of their feathers. The feathers with white streaks, sometimes you can pluck them and they will grow back in darker the next time. Sometimes they grow in lighter. That one with the lightly feathered shanks, you can still use her if she lays nice big dark eggs. She does have "feathered shanks" and will produce feather shanked offspring, of varying degrees of feathering. If you like the more heavily feathered shanks, make sure you get a well feathered roo. If you go too far that direction you end up with feathers on the middle toe, which is another fault to battle. That lightly feathered hen could be your salvation if your flock ends up too heavily feathered in the shanks. Try not to "white knuckle it" with the breeding end of things. Just a lighter hold on the wheel, and enjoy the ride.
Good luck with your new breed. Do keep us posted, ask questions and show pics of how they develop. You got nothing to be ashamed of or stressed over from what I see so far. Hang in there.