Man I hope you're right. It does look like there is a little beige line down the center of each feather on the chest - I might have to go pluck one out of a hen and see it up close!Two, I will have to go read my SOP again (believe it or not I don't have it committed to memory!) but my memory - which isn't very good (and why I don't commit things to it) tells me that "shafting" referred to a different color of the main shaft of the feather. This is easily seen on the back where the shaft of the feather is a completely different color that the peppered partridge feathers. On the breast, I will have to go out and look again but I think what you're seeing in the pics is simply a distinction where the barbules are coming off the quill on opposite side making the quill stand out more and the quill is actually the same color as the barbules.
God Bless,