lol I just like things to make sense if possible.
I have theorized that perhaps since pink hair exists in Narutoverse (along with other unrealistic hair colors), perhaps it's a mutation of red hair, and therefore a pink hair gene could contribute to a red hair gene to make a kid with red hair.
You carry two hair color genes, but multiple eye color genes, if I remember. Naruto would carry a gene for blonde hair, since that's his hair color, and a gene for red hair--since, again, that's all Kushina would have had to pass onto him. Sakura obviously has the gene for pink hair, but she may not necessarily carry her mom's blonde hair gene. Her mom would have had another gene besides the one influencing her hair color--we just don't know what it is.
...don't mind me, I just like talking about this stuff. I'm a fan of science. Hardly an expert, though, so do correct me if I am in error.
Edited by questdrivencollie, 21 November 2014 - 12:31 AM.