Aussie Genetics Fact Sheet
by C.A. Sharp
D-locus dilution, also called "maltese dilute" is probably the most common unacceptable color in Australian Shepherds. A dilutes color will be slate blue in all the places one would expect black or a light shade of brown or red in the places you would expect liver, depending on whether the dogs is otherwise black/blue merle or red/red merle. Since the color of reds is so variable in Aussies, dilute reds can also be variable, ranging from what might be called "fawn" in a Kelpie or Doberman to the pale silvery-beige of a Weimeraner. There will be no true black or liver spots on a dilute. Merles can be dilutes. Blue merles will have slate blue dark patches on a lighter blue background. Red merle dilutes would have medium toned dark patches on a pale red background. Given the extreme variation in red coloration, it is possible that a red merle dilute might not be recognized as such. In a dilute, the exposed areas of skin (nose, eye-rims, etc.) may be somewhat lighter in color than would otherwise be expected.
D-locus dilution, which affects all the black or liver areas of the coat (but not the white or copper) should not be confused with "dilution spots" which are isolated areas of dull, rusty color found on merles. Dilution spots are not disallowed, but they are considered faulty in that the color is not "clear and rich."
Dilute is also seen (and allowed) in Dobermans and Weimeraners, among other breeds. The dilute of black into grey is sometimes called Maltese Blue. The red verision is referred to as Isabella, though in Dobes it is called "fawn."
The gene is recessive, so both parents have to carry it for a dilute puppy to be produced. If a dilute dog were bred, all of it's offspring would carry the dilute gene.
The mode of inheritance for dilution spots is not known, but dogs which have them are more likely to throw them.