Why Does Future Trunks Have Blue Hair Now. There is some confusion as to why future trunks hair is blue in dragon ball super and not purple like in dragon ball z. But that was not the case when dragon ball super episode 47 premiered.
In the anime bulma was given blue hair but for reasons unknown they kept trunks purple hair instead of changing it to blue. Kid trunks hair was also blue and then when it was animated they fixed it and trunk s hair was back to being normal purple. Now we come to dragon ball super and her hair is still blue from dragon ball and dragon ball z but instead of changing it again to purple they change trunks s hair to blue making them both have the same hairstyle now as the manga always did.
This even leads to some characters acting like he had always had blue hair as sort of a hair retcon for the character.
The same with trunks. So toriyama designed future trunks blue haired look and it was not changed. Lately when doing character designs for the anime toriyama tends to give trunks blue hair matching. In the manga trunks and bulma both have purple hair for most of the manga with trunks inheriting his hair color from bulma.