had/has been changing - the change is still happening. The weather has been changing from warm to cold. He is changing from a boy to a man. had/has changed - the change has happened and is finished. She has changed her hair colour from blonde to brown. He had changed from being very nice to very rude.

Jessie, I've just gotten an appropriate answer. Thank you :)

had been changing- this is past perfect continuous. It implies that the change continued for some time in the past before another activity in the past. had changed- this is the past perfect. It implies that the change happened before something else in the past, there is less focus on the time it took. Often we add a duration with past perfect continuous or it might be implied in conversation. The color of the water had been changing for 2 weeks when residents decided to complain. The color of the water had changed so the residents decided to complain.