In older houses, like mine built 1963 they did have black two conductor nm with ground, it is 14/2 solid copper with ground. They used it all the switch legs in the whole house. It aint real easy to see in a dimly lit attic, and I guess that spelled its fall from favor with the electrical field. It could after years in hot attics especially in the southern climates discolor the neutral to a much darker shade, and the outer sheathing may bleed onto the white insulation also. I have never seen this product for sale in my brief 20 year career.
