Here's why it's significant:
* Symbolism: White hair is often associated with purity, innocence, and supernatural abilities. It reflects Allen's role as an Exorcist battling the "Akuma" (evil beings).
* Visual Distinction: White hair makes him stand out from the crowd and emphasizes his unique position as a chosen one.
* Personality: While Allen can be cheerful and upbeat, his white hair also hints at the darker aspects of his past and the burdens he carries.
It's worth noting that there's no specific explanation within the story as to why Allen has white hair. It's simply a part of his character design that adds depth and meaning to his visual presentation.