Dominant Edged or Dominant Silver as the book explains is a dominant gene that converts a bird’s dark melanin pigments to a silver phenotype as the name implies. How it is inherited is autosomal co-dominant, a bird only needs 1 Dominant Silver Gene to display a silver phenotype. This gene heavily reduces melanin and there are varying degrees of dilution of this gene amongst Cockatiels. In some cases, birds are being diluted so much that they are mistaken for Double Factor Dominant Silver and some Single Factor Dominant Silvers display dilution so subtle that they are mistaken for normal at a young age only to become visual Single Factor Dominant Silver after a few molts.
It is considered undesirable to combine dominant edge with other melanin altering mutations as this would result in indistinctive colours that would be difficult to identify – hence the confusion when combining emerald, olive, SFDS, and DFDS. Only test breeding can, with effort, unravel what a bird genetically consists of once this contamination has taken place.