Is fur color change normal in puppies?

So my 3.5 month old Cocker spaniel puppy (working line) was light/medium golden when I brought him in winter. The weather is slowly getting warmer here and I noticed some parts of his ears are becoming way lighter and the fur in his whole body is sprinkled with light and dark golden fur. I was a bit worried if there could be any medical reasons for it? We were at the vets 3 weeks back for his vaccine. Scheduled for another visit in 2 weeks. He was normal during his checkup then and is still healthy otherwise. Just wanted to make sure if this is something that needs urgent attention instead of waiting around for 2 weeks.