What causes the lovely pattern of this sheltie is not a color gene but a modifier to any base color that a Sheltie may inherit.
You take a tri-colored dog, dip it in the merle gene and Voila! You have a blue merle Sheltie.
The gene affects the base color (either the black or the sable) of the dog by causing that mottled, splotched look with varying intensities and shades of color from black to deep gray to silver to light gray (did I hear 50 shades??).
It can also produce an even flecking of the colors as opposed to the large splotches. The dog retains the tan points over the eyes and mouth and legs.
Bi-Blue is different in that it is a black and white Sheltie with the merle gene so the coat is without any tan points.
A sheltie who was sable with the modifying gene and has splotches of sable, tan, and cream in varying amounts. Check out the three puppies on the left. Sometimes they have such faint markings as they mature that it appears a simple sable color. It is not as common as the blue because the possibility of blue eyes is a disqualification in the AKC conformation ring.
This gene can also cause the dog to have one or both eyes blue. These blue eyes are functionally normal. Sometimes one eye is partially blue and partially brown. That is called an “inclusion”.
Sometimes, just to give Sheltie breeders a little more of a challenge when deciding who should be bred to whom, there occasionally is a dog that is a cryptic.
“Cryptic” means hidden. For example, a dog that may appear to be a tri-color sheltie, really carries a merle gene, but expresses it so minimally as to be easily missed.
At one point in time I seriously thought Hope was a cryptic as she produced 2 almost completely white pups when bred to a blue merle.
Both the sire’s owner and I combed through her coat almost follicle by follicle and found a few strange hairs, but so few as to be uncertain if they were simple mismarks or not.
I came to the conclusion that she is not a cryptic but probably both she and the sire are white factored (called piebald in other breeds). Although, strangely enough she has the same red eye reflection in photos that only merle dogs have.
OK Hope, you got some 'splaining to do!
Breeding two merle Shelties has serious repercussions. I'll review that on another page.
A modifier of the merle gene is the harlequin gene which turn the areas that are merle into pure white. Harlequin is a dominant gene. It is extremely rare in Shelties and may be non-existent at this point in time.