
Probably dyed it to disguise himself

Yes. According to wiki this is the definition of the syndrome.
Marie Antoinette syndrome is a sudden whitening of the hair. The event that named the syndrome was the observation that the hair of Queen Marie Antoinette of France turned stark white after her capture after the ill-fated Flight to Varennes during the French Revolution. Witnesses have alleged that Antoinette's hair suddenly turned white on three separate occasions.
Like what happened to Kaneki ken of tokyo ghoul under the repeated torture, his hair turned white.
Though I realize Leon's hair is blond.. so im just putting it out here that this is a possibility. ^^"

i was a wig
Odd, why did he had black hair as a child?