Changing coat doesn’t mean changing color. It means new adult hair is coming in. The adult hair has a different texture and is more curly.
Do you have a picture of your dog with a shaved face ? Having a brownish tint to the hair in the sun might mean the dog is not black but blue. Blue dogs are born black, then slowly face to blue over a few years. Most start around the age of 2, but some will start fading earlier.