Hello,
I'm doing a variant Jubilee project, in that I'm making the line dividing the red feather & the while speckle, blue in colour rather than black. I didn't use speckled sussex mostly because all the speckled sussex I got, had the wrong gene at the e-locus. It is not easy finding good stock in a country this large.
If I understand this correctly you have bred blacks which each carry a mottling gene with a speckled Sussex male? Are the black parent stock which are each carrying the mottling gene homozygous E/E or are they heterozygous E & something else? If so do you know what?