That’s interesting as I am creating a new color of D’Uccles.Mixing definitely is an important step.
But then you have to spend generations sorting out the mixes, to end up with the right combination of traits, and to get them breeding true (no recessive genes to pop up later.)
And if you want them to be accepted by the American Poultry Association, or similar organizations in other countries, you need to check their rules and follow their procedures. They will probably require a written standard, and they might require you to show the actual birds to demonstrate that they birds do exist and breed true, and there may be requirements for having a certain number of other people also raising that variety of that breed-- it varies from one organization to another, but tends to be things along those lines.
Have you got your bird’s recognized by the American Poultry Association?