Is white Siberian Husky puppy a mix or full husky?

Cute. He could be full Sibe. He could be a very Sibe looking mix. Do you have a reason to believe one way or the other?

If he was sold with AKC registration papers, and you have reason to doubt his parentage, you need to contact the AKC.

He doesn't have a blocky enough head to be part Malamute, IMO, or big enough feet. White is a perfectly acceptable color for Sibes (it's in the standard from every kennel club that I know of).

I've got a black and red blanket-back long stock coat German Shepherd. In other words, she doesn't look like your typical, mostly tan Rin-Tin-Tin type German Shepherd that most people are used to seeing. Doesn't change the fact that she's a German Shepherd.

And for what it's worth, I've got friends with champion show dogs who have had people insist that their dog was obviously some other breed entirely.