|Image provided to me by J. Burns of Ghostfire Photography, and is copyright to him|
Here's a couple more pictures of Petey (taken at a boarding facility). Click for the full size images.
Petey is a pit bull mix who actually has a nearly completely white head! This is a bit odd, since otherwise his white is fairly minimal. From what I've seen, this is actually a fairly common occurrence in pit bulls, bulldogs, and mixes of similar type, where the dog has far more white on its head than would be expected when looking at the amount of white on its body. This is likely due to selective breeding for this phenotype. The genetics behind facial white is not very well understood, but the variation seen (both this extreme, and the opposite extreme of color-headed white) is likely due to the action of plus and minus modifiers. Plus modifiers would allow more white to occur, while minus modifiers would make less white occur. With the addition of selective breeding, this would explain how some breeds (or sometimes certain lines in a breed) have achieved fairly consistent amounts of facial white. Anyway, on to Petey's likely genotype:
This dog clearly has tan point, and as such must be atat tan pointed. I do not see any evidence for recessive black in pit bulls, and as such it is highly unlikely that Petey carries this color.
In pit bulls, it is common for dogs to be called "red-nosed" or "blue-nosed," which simply means that they express one of the dilutions that turn black in the coat to liver or blue, and which will affect the skin pigment as well. Petey appears to be a nice, deep black, however it is quite possible that he carries one of the color dilutions. Due to this, I am going to claim that he is Bb non-liver carrying liver and Dd non-blue carrying blue.
The only other gene that is likely to be affecting his phenotype is the spotting gene. Though he has so much white on his head, if you ignore his face he is actually collared Irish white. Though it is possible he is carrying a piebald gene, since piebald is also common in pit bulls, I don't think it is likely. I am told he doesn't have any white past his shoulders except for white toes. So, I do not believe that he carries piebald. That would make him sisi white collared Irish.
So, that would be atat Bb Dd sisi or white-faced collared Irish black and tan (carrying liver and blue).