Board Thread:Naruto Discussions/@comment-45255175-20200501155826/@comment-32685487-20200502002838

Because the whole Uzumaki have red hair thing didn't come about until later in the P2 of the series.. after Naruto, Nawaki and Tsunade were already introduced. If the red hair thing was a fact from the start theres a high chance all 3 of them would have had red hair.