Were Aussie colors in the early years the same as they are now?
For the most part, with a marked preference for blue merle. But many years ago, before the current standards were set, there were all sorts of colors and patterns in Aussies: piebalds, brindles, sables, and saddle-patterns (like a German Shepherd Dog or Airedale,) as well as yellows and dilutes. The precursor of all the breed standards we use today was written in the late 1970s, establishing black or liver, with or without merle patterning and with or without white and/or tan trim as acceptable colors for the breed. Since then breeders have been selecting away from all the other colors and patterns. Some are gone entirely, but those that are genetically recessive (yellow and dilute) still appear from time to time.
How many different color genes do Aussies have?
The same number as any other kind of dog. That said, which ones are most important varies by breed and for some breeds like the Schipperke or the Weimaraner, which are all a single coat color, it isn’t much of a topic at all.
What genes are important for dog coat colors?
As of this writing (2019) there are eight identified coat color genes all of which Aussies can have more than one version:
A locus (agouti)
B locus (brown)
D locus (dilute)
E locus (extension)
K locus (dominant black)
M locus (merle)
S locus (spotting)
Of these only B and M are highly important in Aussie coat color genetics; A, K, and S cause minor variations; and E and D can result in disqualifying (non-standard) colors. H is specific to a color pattern found only in Great Danes and not to be confused with the tweed merle pattern variation in Aussies sometimes called by that name. ASHGI uses “tweed” because this was the name that it was given when first described in the scientific literature. It also avoids confusion with the Great Date color pattern called harlequin which is due to a separate gene which acts on merle.
There are several other genes that are assumed to exist based on long study of canine coat colors and patterns for which no specific gene has yet been identified. One of these, the T locus (ticking) is clearly found in Aussies and causes color spots within otherwise white areas.