User blog comment:Lordranged7/Voting for Pics/@comment-4726368-20121130195808/@comment-4928091-20121130200137

I think 3 reasons,

1. He inherited that hair colour from one of his relatives, mabye Tenma marrys a girl who is blonde and she passes her hair colour onto him.

2. Level 5 made him look like that to trick us into thinking he was Gouenji Masato or one of Shuuya's relatives.

3. He is Tenmas relatives but he wears a blonde hair wig to disguise himself when he meets Tenma.