I will let the original poster reply but I understood him/her to mean the ducks pictured father not grand father could be any of the three.
Are you saying that a drake produced from a cross between an Appleyard and a Pekin should have a white throat? Does the white throat come from the...
Do you mean you crossed two white ducks and got other colors? That would be unexpected. If you mean you crossed two that were half Pekin, that would make sense. There would only be a 25% probability of a duckling being white. In the original poster’s case, the mother is white. If the mixed...
So, dad is not the Pekin, the babies would all be white. Dad could be the Appleyard or the mix. I would suspect the Appleyard but it could be either. The black color could be from the Pekin mother. You might enjoy looking at other peoples different mixes on this post: mixed-breed-ducks.
Pekins and other white ducks have two recessive alleles which causes no color to be put in the feathers. They can then be carrying any other color "underneath". So, there is really no way to know what else the Silver Appleyard mix was mixed with except it probably wasn't white if there wasn't...