Totally normal. Happens in a lot of Goldens. Cold weather is certainly part of it, and I have heard that bowls could make a difference, though I can't remember which way it goes (which kind of bowls may help cause the nose to change colour). Also, I can't say for sure that the bowl thing is true - it is something I've heard though. I have seen the depigmentation progress as dogs age too.
My Retriever pup (not a Golden this time, but a Nova Scotia Duck Tolling Retriever) is going through his first winter and his nose has changed colour a tiny bit, but not much.
"If you're not chasing after miracles, what's the point?" The movie Saint Ralph
"What it all comes down to
Is that everything's gonna be fine fine fine
I've got one hand in my pocket
And the other one is giving a high five" - Alanis Morisette, Hand in My Pocket