Mack Snows are all black and white when they hatch, when they grow up they can sometimes look like a normal, the only way to tell then is to breed them.
(Of course there also are normals, that look like snows)
If you're looking for some, let the breeder show you pictures of them as hatchlings, or buy them at a young age, and you're good to go
And if you're breeding them anyway: you could show us pictures of them
yours,
Fabrizio