Are the stripes in his coat black or blue? If he's blue brindle, he'll have nothing but blue pigment. (Blue dogs can't produce black pigment, because of the dilution gene.) If there's black in his coat, then he wouldn't be a blue brindle. On the other hand, there are things that will break down the pigment in a dog's nose. Our Dogo started out with a jet black nose which broke down to purple as he aged.
Ok- so I have to say that I have seen a blue nose brindle but they have been the blue brindles. I have never seen one with the coloring of my male so I guess I should have phrased that differantly.
My boy has the black stipes so he's not the blue brindle. As I remeber his nose has always been this color and I have had him since he was a baby. And I am not sure what the parents looked like. Could he have blues in his background somewhere that just showed up in his nose only? Gosh-maybe he's just a freak of nature with his odd nose! lol