I raise Australian Spotted ducks from Holderreads so I would say these are probably Mini Appleyard, which is a breed we considered but we went with the Spots. We have had some silverhead Spots with white backgrounds but the spot color is not as dark as your hen. With Spots the greenhead hens have brown spots, the bluehead hens have blue spots, and the silverhead hens have silver spots that fade into the background color, which is typically darkest in the greenheads and lightest in the dilutes. The spots on your hen look black.
It could be that the same color genetics cause the white background color in both breeds but it is uncommon in the Spots while it seems to be a more typical color in the Appleyards. The Australian Spotted drakes actually get spots but they are only visible part of the year so sometimes they are in eclipse phase and sometimes they look more gray colored.
The Spots should have orange bills and feet so dark colored bills are not in line with the standard. Our white Spot hen had a darker bill so we did not keep her but when I asked Dave Holderread about her color he said she had the harlequin genetics which produces more color. We kept her daughters because their bills are lighter but it is a concern that the dark bill could return. I don't know enough about genetics to know if we should have culled her from our breeding program so I am trusting Dave's opinion that her color is desirable for breeding.