It could be for a girl. Perhaps there's a girl he likes who has a preference for guys with unique hair colors. So, Draco decides to dye his hair to catch her attention.
He might be influenced by the Muggle world. After some interactions with Muggles or learning about Muggle culture, he becomes fascinated with the idea of dyeing hair as it's something very different from the wizarding world's usual appearance norms.
Maybe he wants to rebel against his family's traditional image. In the wizarding world, the Malfoy family has a certain 'pure - blood' and proper image. Dyeing his hair could be a way for Draco to show his individuality and break free from the constraints his family has put on him.
Maybe he wants to change his look to disguise himself from his enemies. In fanfiction, there could be all sorts of threats and he might think a new hair color would help him blend in or not be recognized so easily.
One reason could be for a disguise. Maybe she's on the run from some bad guys in the fanfiction world and changing her hair color helps her blend in better.
In fanfiction, it could be related to a magical accident. Maybe a spell went wrong and changed the color of his hair, and then he decided to keep it and even dye it a different color on purpose. It could also be a part of a transformation arc, where changing his appearance, starting with his hair, is a symbol of his growth and change as a character.
He could dye it black to look more mysterious, like a dark wizard in disguise. Or perhaps he'd go for a bright red, which would make him stand out more and show his boldness. Another option could be a platinum blond, giving him a completely different look, maybe to imitate a famous wizard from history.
One possible reason could be his father's strict and cold parenting style. Lucius Malfoy was often very controlling, pushing Draco to uphold the family's pure - blood ideals and reputation, which might have made Draco feel suffocated and resentful. Another reason could be that Draco witnessed his father's dark deeds in the wizarding world, like being involved with Voldemort, and he might have moral objections to such actions.
One reason could be for a disguise. Maybe he's on a secret mission and needs to pass as someone else. Another could be peer pressure. His friends might have dared him to do it.
Green hair dye was a trendy hair color choice. There were many different green hair colors to choose from, such as mint green, peacock green, matcha green, dark green, and so on. These green hair colors could show different styles and personalities, from the noble and pure emerald green to the fashionable peacock green, which could bring different visual effects. In addition, green hair dye could also be chosen according to one's skin color and preferences, such as low-key and gentle green tea, avocado green, grass green, and so on. For boys, dyeing their hair green could show their personality and fashion sense. In general, green hair dye was a popular hair color choice. You could choose a green hair color that suited your personal preference and style.
Fei Xiang's hair was not dyed black. His hair was black. Fei Xiang was of mixed Chinese and American descent. He had inherited his father's tall and handsome figure and his mother's black hair. His black hair made him look handsome and young.
Well, it might be because of a magical accident. Maybe he was experimenting with some dark magic that backfired on him. Or perhaps he was using a powerful spell without proper training. Also, in fanfiction, it could be related to his health. He could have an underlying medical condition that hasn't been discovered yet, like a weak heart or some sort of magical malady that causes him to faint when he overexerts himself magically.
Perhaps in the fanfic, Naruto is trying to fit into a different group or culture. His original hair style might make him stand out in a negative way in that context, so he changes it to be more accepted. Or it could be part of a bet or a challenge. For instance, he loses a bet with his friends and as a consequence, he has to change his hair style.