Hope you're able to hatch a ton off those dark layers!! BEST of luck for a really good year!!
It's been said that the W. Jeane line has recessive wheaten in it. Some folks look at that as a bad thing, but from I have understood, that's where we got our wheaten variety, from a sport out of that line. I got some Black Copper hatching eggs from
Linda Hamid in California about 5 years ago - quite nice birds, and good, dark, eggs (and she's a lovely person to work with...however, I believe she's gotten out of Black Coppers now), and I hatched two wheatens from those eggs. I sort of wish I'd have kept them now - both were pullets and I wasn't interested in anything that wasn't Black Copper at the time, so I sold them as layers. I hear tell those birds lay uber dark eggs, so someone may have gotten quite a surprise when those birds began to lay for them!
Again, there is not a lot of research that's been done on egg color, so I honestly don't think anyone can answer this question with a huge degree of certainty. It does seem that it's common for the first generation of a newly added line to an existing line for some folks (maybe for many?) produces females that dont' lay quite as dark as the parent stock; however, that F2 generation, when bred back to the father/cock bird, does seem to pull some of the dark genetics for the eggs back in.
For sure, the whole dark egg thing isn't any easy one to work on...if it was, we'd all have 9's in our nest boxes every day, eh?