A friend of mine has a half BC/half Aussie, a very nice dog that I helped her
start in herding. I know that a lot of ranchers like this blend. She got
this great dog out of a box of puppies being given away at a local grocery
store! A couple of times I've had people call asking where they can find
this particular cross.
I believe the black in Border Collies is by and large the dominant black,
although it's possible there may be some of the recessive variety that is
known to occur in Shelties, GSD's, and which we know now still does occur,
although very rare, in Rough Collies.
Merle, being dominant over all colors (it's a pattern that affects the base
color, rather than being a color per se), requires a merle parent. An
offspring of a merle that wasn't merle itself would have no merle gene to
give to any subsequent offspring, thus genetically there would be no
difference between a tricolor from two tricolor parents, and a tricolor from
one merle and one tricolor parent.
When flecks in white markings occur, they occur in the color that the leg,
muzzle or body would be if the white markings weren't there. Thus, a black
dog will have black flecks, a black and tan dog will have black flecks where
the black would be and tan flecks where the tan would be on the legs or face
in the black-and-tan pattern (which, with white added, becomes tricolor).
Apparently there were black-and-tan pattern Dalmatians at one time (there
still may be on a rare occasion, since black-and-tan is recessive to black
and thus can be hard to breed out entirely); these had black spots on the
body and tan spots on the legs and the sides of the muzzle, which were
faulted of course in the show ring. The regular Dalmatian is simply a black
dog, the recessive liver dalmatian a liver dog (brown spots all over with a
Border Collies and Aussies, being essentially of the same working collie
background, share the same colors, except that sable has come to be faulted
in Aussies although I have heard of it still occurring on occasion, and I
have seen a couple of photos of saddle-pattern Aussies. A merle
saddle-pattern would have the most noticeable merling in the saddle area, and
just as the saddle pattern ES and Collie have been called tricolor, the
saddle-pattern would probably be considered a merle -- just a merle with
extensive tan trim. The tan areas would also have some merling, but the
contrast between dark tan and light tan isn't as noticeable as the contrast
between black and grey.
The color patterns in the Aussie X BC litter accords to what would occur in
an all-Aussie or all-BC litter, when breeding tricolors to black-and-whites.
In this case (just speculation, but going by what's typical), the black is
probably the dominant black, carrying the black-and-tan pattern (tricolor)
recessive. When bred to a tricolor, both black-and-white and tricolor
puppies would be likely. I believe flecking (ticking) is generally a
dominant, so if one parent was noticeably flecked, many or most of the
puppies would be (how many would depend on whether the flecked parent carried
the recessive "no ticking" gene). The extent of flecking is apparently
determined by modifiers that allow less, or more, ticking to be expressed.
Ticking is fairly common in BC's, occurs to a certain extent in Shelties, is
less common but does occur in Aussies, and even less common, but again it
does occur, in Collies. Although ticking, especially heavy ticking is
associated most often with gundogs, I have seen extensive ticking in such
diverse breeds as Akitas, fox terriers and St. Bernards. "Blue" and "red"
heelers (Australian Cattle Dogs) are very heavily ticked dogs, the ticking so
heavy as to have an almost solid appearance. Photos of earlier Cattle Dogs
show more of the white base -- something like the "belton" English Setter