They change their colors all the time (Brady is 3 and still is)
Attitude is all in how you train, raised and socialized the pup.
as far as growth it all depends I know Brady height wise stopped growing whenhe was 18 months. But he developed fully bye 3ish (muscle)
I have a three-year-old female, and I remember that when she was about a year old, she became very serious about protecting our yard. When she was very young, she used to just sit quietly and watch people go by. By one year of age, she would run back and forth along the fence with her hackles up and, literally, frothing at the mouth! Looked very scary! But other than protecting the yard, she has a wonderful temperament. Typical GSD aloofness, but very easy-going with humans.
Now, dogs are another story. As a pup, I would take her to the dog park daily, and she loved to play with other dogs (although she always played very rough). Between a year and 18 months, she seemed to enjoy playing less and was becoming more aggressive. She has a rather dominant personality and seems to like her space. We respect that and don't expect her to romp around with other dogs, but we do insist that she behave when they're around.
Someone told me when she was a puppy that I would see her personality change as she matured, and they were right. I'd say just work with any issues as they come up. And look forward to a gradual decrease in energy levels!