During the movie, Sophie for the most part was seen in the form of an old woman, thanks to the curse the Witch of the Wastes cast on her. However, whenever Sophie slept, she seemed to revert back to her regular self. And when she was talking to Madam Soloman, her body was slowly reverting and her hair was changing colour. Also, when Howl was setting things up for everyone, her facial features and voice reverted but not her hair.
By the end of the film, Sophie still had white hair but she seemed to have regained her youthful appearance. However, the Witch of the Wastes never removed the curse, given her magic was drained. I am wondering if Sophie's curse was eventually dispelled or not.