Sibes do the same thing. Usually they start out light, go super dark, then progress more white as they age, thus why many lose their face masks.
Many GSDs I've seen changed dramatically, too. Didn't notice until Gustav came around. Goose was GSD/Sibe and he creeped hard. Completely dark and pigmented to blonde and tan with a snow nose by his first year. This is just 6 months progression. He's gotten lighter.
As a pup:
Belly shot: