To me, a tux kitty is ALL black on top, with white maybe on the face, a white "shirtfront (which may lead all the way to a white tummy, and white "spats" or feet. Tuxedo isn't a breed, by the way, just a color pattern.

Fluff's breed is probably "mixed" but I agree that her pattern is cow kitty!

(I grew up in a neighborhood with a grand dame polydactly tuxedo mama kitty, so most of the kitties in the neighborhood looked like her - their Mama, grandmam, etc.)