I will make my two cents comment right about now: Since currently you are willing to spend money on DNA Testing, why don't you just keep breeding back to pure Wyandotte? Get rid of the autosomal red that is on your stock, improve body and feather type orders of magnitud faster than what you...
Leghorns have shell color diluters to make their eggs extra white. When crossed with Brown eggers like Wyandotte or Australorps the hens lay white eggs, for example the AustraWhite hybrid cross the hen lays nearly white eggs