Interesting...I've got what I was told was a Dark Brahma hen with that same pattern.
Bee, they are Silver Pencil Rocks... here are 3 of the 4 girls with their mixed up group ...2 hens hatched one week and are completely co-brooding their hatches, the 3rd hatched a week later and has daytime visitation and co-parenting duties but as of now still keeps her younger ones all under herself at night... the 4th one is now waiting for her clutch of eggs, which my hubby and I are picking up Friday morning for her.
I also have 4 other broodies, 2 easter egger mixes, one black giant and one very silkie looking girl (maybe a mix though).