The double lace may very well be from Cornish infusion. It could be bred out if you have the desire and are willing to work with it.
As for the black in the hackles, if that is where you are seeing it, your birds are still young and most of it will either get covered by growth of adult feathering or blend in. It is not uncommon for me to see that and when they are adults, you have to actually look under the abundant hackles to see any of it. These birds change A LOT between 5-7 months, you may be amazed. If I see black in the shoulders or too much coming out on the wings other than primaries, or surface black on the breast, back or between the legs, or coming out in the fluff, those are bigger concerns for black at this point in their development.
As for the black in the hackles, if that is where you are seeing it, your birds are still young and most of it will either get covered by growth of adult feathering or blend in. It is not uncommon for me to see that and when they are adults, you have to actually look under the abundant hackles to see any of it. These birds change A LOT between 5-7 months, you may be amazed. If I see black in the shoulders or too much coming out on the wings other than primaries, or surface black on the breast, back or between the legs, or coming out in the fluff, those are bigger concerns for black at this point in their development.