One distinction to make here is what you are calling Wheaten. There is only one wheaten gene that makes a Marans "wheaten", and a Black Copper may display white shanks, less black in the hackle, brown fluff in the bum, and red on the chest of roosters without having the wheaten gene. These faults have been collectively called "wheaten influence", or what can be the leftover faults when there is wheaten in the background.
White shanks and red in the chest do not mean you have a wheaten Marans. But they can suggest they may be carrying the wheaten gene, and are at least faults that can originate from wheaten being bred to BC.
Things are a little different here in Europe, and I have seen pure BC with good dark copper colored hackle with only a bit of black striping, and most of the pure black copper roosters have lighter shanks than what I have seen in U.S. bred BCM. So these traits can be found on pure BC as well.
There is a gene called Darkbrown, that produces brown headed chicks, when they should be mostly black. This gene is not from wheaten, but can cause brown fluff or extra red in the breast or shafting/mossiness throughout in adults. This gene is fairly prevalent, and often goes undetected in hens, so mark and don't use any birds that started out with brown heads.
All this to say, if you see faults they don't always mean wheaten in the bird you are looking at. They may just mean wheaten in the parentage. Also, just because you are seeing blue doesn't mean you have wheaten, you may just have some blue copper parentage.
But starting over with very good stock is always the best solution. You're in the right place, and asking questions and learning is the best first step before beginning again.
I don't go to the big Marans thread very often, I don't get enough laptop time to follow it, though amidst the friendly chatter there are tons of great things to learn. I spent a couple years following it, and learned a lot. If you have the time, there's good people and good stuff there.
