Like most anime, Dragon Ball has characters who were born with rather abnormal hair colors. People with blue, purple, green and even pink hair are a common sight in this world, including prominent heroes such as Bulma and her son Trunks. Bulma is known for her blue hair with a variety of styles, but both Future Trunks and Young Trunks were known for having purple hair in Dragon Ball Z.
This changed in Dragon Ball Super, where Future Trunks suddenly has the same blue hair color as his mother -- yet his present-day counterpart still has purple hair for some reason. Here's a look at the history behind Bulma and Trunks' hair and how the latter's coloring has become so confusing.
Bulma's Hair Color
Unknown to many fans, Bulma's hair in the original Dragon Ball manga is actually purple. This particular shade of violet heavily resembles the hair color that Trunks would become known for as well. In the first chapter of the manga, however, her hair is colored in as blue, leading to the anime using that instead of purple. It's worth noting that Bulma's father, Dr. Brief, also resembles his daughter's light blue hair color on the show.
When Trunks was introduced in the manga, he was drawn (in colored images) to have the same shade of blue hair as his mom. When the anime adaptation of the later Dragon Ball Z stories came along, however, Toei decided to give Trunks Bulma's original hair color of purple instead of blue. Nice and simple, right?
Future Trunks' Hair Color
Dragon Ball Super would attempt to rectify this by giving Future Trunks blue hair as well. His hereditary hair color finally made him look like both his mom and his maternal grandfather since he didn't have the brunet hair of his father's genetic line. This actually makes him an outlier, as Saiyans usually have dark hair instead of blue/purple tresses. In fact, people act as if he's always had blue hair, even though fans of the anime recognize him better with purple. What isn't explained, however, is why Young Trunks of the main timeline still has purple hair.
This seems to be a random choice or perhaps even laziness on Toei's part, as Akira Toriyama's character designs for the Dragon Ball Super anime even gave Kid Trunks blue hair instead of purple. It may be to keep in line with just how iconic Trunks' purple-haired design is, as almost all previous merchandise showcases him with this color. Thus, previous toys and statues of Kid Trunks with purple are still "accurate," even if it doesn't match his older counterpart.
