It could be related to a specific event in the fanfic. For example, if she's going undercover for some mission, changing her hair color might be part of her disguise. Also, perhaps she's influenced by someone she admires and decides to copy their hair color.
She might choose blue. Blue is often associated with intelligence and mystery, which suits Hermione well. It would be a bold yet still somewhat sophisticated choice for her.
Well, there could be a fanfiction where Bella dyes her hair purple by accident. Maybe she was trying to use a natural hair treatment but something went wrong with the ingredients. Her friends are initially shocked but then they start to love her new look. This new hair color also catches the eye of a certain character who previously hadn't noticed her much, and it sets off a whole new series of events in the story.
It might change her relationship with Ron. He could be initially shocked but then grow to like the new look, seeing it as a sign of Hermione's independence. Or it could cause some tension if he preferred her old look.
In this fanfic, Sakura coloring her hair might be part of a self - discovery journey related to Sasuke. She might start with her natural hair color, feeling a bit ordinary in Sasuke's perception. So she takes the bold step of coloring it, perhaps a bright pink which is more vibrant and shows her new - found confidence in her love for him. This change in her appearance could lead to various interactions with Sasuke, from his initial surprise to a possible deeper connection as he starts to see her in a new light.
Hermione could also be very hurt. Her hair is part of her identity, and having Draco, who she already has a strained relationship with, do something so cruel would cut deep. She might go to her friends, Harry and Ron, for support. They would likely be just as angry as she is and plot some sort of revenge against Draco and his Slytherin friends.
One possible reason could be a symbol of a new beginning. Maybe she's had a major life change, like starting a new chapter in her relationship or in her studies at Hogwarts. It could also be a sign of rebellion against the traditional image others have of her. In some fanfictions, she might cut her hair to fit in with a different group or to show that she's breaking free from her old self.
Shikamaru might just sigh and say something like 'What a troublesome thing to do, Naruto.' But deep down, he would also be a bit curious about why Naruto decided to dye his hair red.
She would probably be very angry. Hermione is a strong - willed character. She might immediately try to break free from his grip and demand an explanation. For instance, she could shout at him, 'Professor Snape, what do you think you're doing? This is completely unacceptable!'
Maybe he just wants a new look. Naruto is always known for his wild and adventurous spirit, so dyeing his hair red could be a way to show his rebellious side or simply to stand out more.