Misato’s hair, despite being depicted as dark purple in the anime, is presumably black “in universe*”, just stylized as purple for the audience’s benefit. Rei obviously has unnatural blue hair, but nobody really seems to comment on it. The idea of “unnatural” hair colors is also touched on with Ritsuko, where it’s revealed that she doesn’t in fact have anime hair, she actually just bleached it blond as sort of an act of rebellion against her mother.

Is it possible that Rei’s hair is not, in fact, literally blue in-universe, and that it’s only depicted that way to make her character design more interesting? Perhaps in-universe she actually has white/silver hair like Kaworu, which while still unusual, is at least attributable to an existing medical condition and wouldn’t draw excessive attention.

Yes I’m aware this is kind of a dumb “question” but it is a line of thought I’ve wondered for a while. After all I think it’s kind of unusual that literally nobody makes any mention of her hair color, and you’d think that anything hinting at her alien origins would have been covered up by Gendo.

* In this instance I use “in universe” to mean the “actual world where the characters live in” vs. “the abstracted fictional anime representation of that world” that we view as the audience.

For a funny coincidence, I went to Japan one time to ask a doujin artist if I could marry his character. When I was asking him questions about how he designed her I asked "Since she has blonde hair and blue eyes is she a half or something?" He laughed and said "Well in anime characters like Rei have blue hair so it doesn't matter right?"

More on topic, there's a few strange things with hair color in universe. Gendo is 48 and doesn't have a single grey hair. I suppose there's always hair dye but I assume it's just normal in their universe unless otherwise stated, see in Slam Dunk when teachers scold Hanamichi for having dyed hair.

This used to be a big topic of contention back in the day, and still popped up every now and then when I first joined.
To which I say: What makes you think that it wouldn't be her in-universe haircolor? Because it's not possible for a human to naturally have blue hair? Well, neither is it possible for a human to be 80 meters tall and procest impenetrable defense fields. It's anime, it doesn't work by the same rules as actual reality does.

Any attempt at finding a reason why Rei would have a different hair color in-universe inevitably turns into something patently ridiculous, especially the argument of "oh she has normal hair color, but it's just to cue the audience in that she is different"; Kaworu is also very visibly different, and he has white hair. Why on earth would Rei be any different if that was the intent?

Yep:

Like when you have anime where entirely western characters are speaking Japanese and adopting Japanese mannerisms, you kinda have to let go and accept that you are watching a cartoon - a very anatomically correct cartoon - but a cartoon nonetheless. No mouse has ever looked, stood, dressed, or spoken like Mickey Mouse, but he's still "a mouse". Krillin was designed without a nose, but of course he has a nose, yet characters have pointed out that he hasn't got a nose. Or tanned/dark skinned characters and fans will speculate what non-Japanese nationality they might be, but they're really just designed to appear as such. Things are designed for their medium.

I’m pretty sure it’s genetics, with her being part angel and all.

Blue hair in the eva universe is uncommen but some do have it, altough it's more purple. Early designs had her with jet black hair, perhaps to oppose with Kaworu's white hair but presumably the figurines head would look to much like Shinji (or not stand out enough).

I believe they chooce blue because they wanted her profile and figurines to both oppose and compliment with Asuka's.
Rei has blue hair and red eyes, Asuka has blue eyes and red hair.

Having Rei be somewhat of a mother figure to Shinji, similar to Misato probably inspired it, but Rei would look to similar like a child clone of Misato.

Ultimatly I would say that it's her real hair color but it isn't blue it's purple but despite being confirmed she is not a albino she doesn't produce enough melanin probably making her OCA2. Given that Rei isn't visually impaired her eyes probably aren't red but brown OCA2:GA1

I’m far more of a fan of the question: “What do we the audience gain by Rei’s hair being blue?”

If that question has an interesting answer, then it’s a solid argument for the blue hair. If that question doesn’t have an interesting answer, then it really doesn’t matter whether or not it’s blue.

And I think the wild hair colors for Rei and Kaworu (hinting at their similarly unusual origins) are more narratively interesting than whether or not Misato’s hair is purple.

The models in this ad give a plausible set of "real world" hair colours.

tweet-body

— twitter-user (@username) date

thx Mr tines not exactly canon but interesting non the less

FreakyFilmFan4ever wrote:I’m far more of a fan of the question: “What do we the audience gain by Rei’s hair being blue?”

If that question has an interesting answer, then it’s a solid argument for the blue hair. If that question doesn’t have an interesting answer, then it really doesn’t matter whether or not it’s blue.

And I think the wild hair colors for Rei and Kaworu (hinting at their similarly unusual origins) are more narratively interesting than whether or not Misato’s hair is purple.

Okay Rei is stated as a girl that has emotions but has difficulty showing them/ understanding them (https://forum.evageeks.org/thread/16407/Reis-Deal-Emotions-No-Emotions/)

if Rei colors her hair, there's a bid of hipster punk rock in the character and she does stuff to get noticed in public, my opinion she doesn't color her head hair but she does colors her eye lashes to apear more human (albinos have white eyelashes) So Rei spends a relative large amound of attention on her appearance (to look normal)

Sadamoto said it highlighted her personally best I believe altough I can not find the source

blue hair and red eyes I assume means angelic and human properties. It would be weird if she looked like mini-Shinji's mother.

I used to trip over this stuff all the time, thinking how creatures in Zelda games perceived one another hahahaha! Now I see that I was a very weird kid.
Yeah. Ayanami has Blue hair, Goku has huge eyes and Mario is, well, the way he is... XD

I beleive Mario is antropomorphic not the worst in the mario universe like what exactly are the Mushroom People?

As confirmed by Kenta Motokura (Super Mario Odyssey's director), Mario is just a different type of human. There are more realistic humans in addition to people like Mario.
I would say Toads are mushroom people. Which is funny, because they're ruled by Peach, who is a human just like Mario (or so it seems). So the mushroom people are not represented by someone of their own race XD

shouldn't link be death or something he was a sort of elf that shouldn't have been able to leave his forest or something I don't know enough of the topic honnestly I remember something on game theory

Blue could have been associated with water and gives artistic sense of clearness or lacking in color, without the hair actually being clear or lacking in color. It then represents Rei's lack of energy, or lack of color to her personality, or lack of social development for her age, but she still has a clear sense of who she is (a science experiment) and what her mission is (pilot the eva's and defeat the angels).

Kaworu's white hair would then denote that his personality has a sense of fullness and energy, since white is the combination of all the colors in the visible spectrum. It also has a tinge of purple. Since purple is the highest color on the visible spectrum before it heads towards Ultraviolet where any higher light-frequency would not be visible to the human eye, the purple tinge could represent his FAR-like origins/properties, since FAR can interact with higher dimensions that humans have no access to even scientifically. Perhaps Rei has a tinge of purple in her hair as well.

Regarding why people in Tokyo-3 don't seem to mind Rei's strange hair color, this is gonna be far fetched and maybe not intended by the author's of NGE, but Nerve and Magi have manipulative control over Tokyo-3's government and society, including the types of propaganda citizens might read about or encounter. If Russia can convince themselves Western Europe is full of Nazi's, then maybe Nerve/Magi can convince the average student in Tokyo-3 that blue hair is very rare but still normal.

I ask again: In a world where the apocalypse has happened and eldritch horrors are fought using other eldritch horrors clad in steel plating, is it really that hard to believe that some people would just have hair color that people can't have in real life?

Blockio wrote:I ask again: In a world where the apocalypse has happened and eldritch horrors are fought using other eldritch horrors clad in steel plating, is it really that hard to believe that some people would just have hair color that people can't have in real life?

It’s not “Rei having blue hair” that is the problem, it’s literally NOBODY even hinting that it might be an unusual quality, or ever even mentioning it at all. In most anime it’s just accepted that people have wacky hair colors that are apparently natural, and are never be addressed in-universe, but Evangelion specifically averts this with its character designs with the vast majority of its cast just having black or brown hair and the exceptions being explicitly addressed (Asuka is a foreigner, Ritsuko dyed her hair to distinguish herself from her mom) so I think it’s fair to ask why the only character with objectively un-natural hair color is never pointed out as being unusual.

The only explanation I can think of is that maybe Rei has been at the school since she was a child (I don’t actually recall if she’s implied to have been there the whole time or if she just recently transferred in), and all the kids got over the whole “blue hair” thing years ago.

While I don't have the quote to hand, it was definitely implied that she had been another comparatively recent arrival to the class (not just in episode 26).