We have a golden retriever who is 1 1/2 yrs old. Her nose was black when we got her but changed to a pinker color during the winter. I was concerned about this but found out from other GR owners that it is usually referred to as a "snow nose".
Pigmentation is sometimes lost during the winter months due to lack of sunshine. Not all dogs lose the black and some lose more than others. I was told that some dogs will get their black nose back completely in the summer, others will get most, some never get that black nose back at all. They also said that as the dog gets older each season could show less of the black coming back in the summer.
Maggie's nose is almost all black again now.