Porcelain is a lavender bird with the gold gene and mottling gene. Mottling and lavender are recessive, so all the offspring with one porcelain parent will be split(carrying) porcelain gene.
Golden neck is a millie fleur with 2 blue genes.
Here's what your offspring will look like
Golden neck X black mottled = blue millie or blue mottled, I think. And golden neck X porcelain = blue mottled or blue millie split to porcelain.. I think :)