We know that there's not a lot of people born a natural purple or with rainbows on their heads, neither as much into dying their heads into crazy pastel-y colors.

Since I'm new to this humanized, how do you guys deal with hair colors?
I though of giving the mane six natural colors that in spirit are the same as the pony's manes but aren't the same.
Like both Rarity and Twilight having black hair, Pinkie being a redhead and Rainbow Dash either white or grey hair and Fluttershy having light orange hair, but I'm still not sure about how is generally handled.

In fan art, at least, I've seen it done all sorts of ways. Write whatever you feel like.

Generally hair stays true to the show, keeping all the crazy colors.
But if you want to go and make them much closer to human instead, go for it.
Changing It isnt the norm if thats what youre asking, but I doubt anyone will get too upset if you want to change it.

I prefer sticking with the original colors and would write them as such if I made a human story, but there's nothing wrong with such a change. Go for it. lol

I just stick with the original colors, and do variations in the style.
Example: I write Dash with very short (sometimes buzzed) rainbow hair, and Luna with a blue ponytail.

938596

Rainbow Dash either white or grey hair

Unless your humanizing them as middle-aged/older, white or grey isn't a whole lot less crazy-animu style than a rainbow.

Most of the humanizations I've seen keep the original colors. If you want natural colors, then it really depends on how you've humanized their personalities. Is your humanized Dash a biker or a punk or a navy/marine/air force pilot, or whatever? Same with Pinkie, either one could be into a scene where dying your hair crazy ass colors makes perfect sense. Or (in the case of a military Dash) in a position where crazy colors is verbotten.

Also, don't forget strawberry blond as an option.

Unless your humanizing them as middle-aged/older, white or grey isn't a whole lot less crazy-animu style than a rainbow.

I did considered that and didn't discarded it on the basis that Dash is always special.

Most fics seem to retain their in-show color, and even on-Earth fics don't seem to question it. I have yet to see a fic that explicitly says that their hair is dyed, instead opting for, "That's just the way it is. Moving on...". I still have yet to find a story where natural-colored hair is used, but that's something that could help a fic stand out.

Personally, there's no problem with having funny-colored hair in a humanized fic (especially since anime standardized the trend of hot-pink hair), but I think it's a missed opportunity to say something about the character. In my eyes, dying someone's hair color from its natural hue to something unnatural lends something to the character and implies that there's something about themselves that they want to change or hide. I have yet to see anyone explore such an angle (except for mine in planning).

I usually see fics with the original hair color, but a few have altered the colors to be closer to natural hues with a few abnormal undertones. However, Rainbow Dash seems to always retain her natural multichromatic pattern.

Occasionally they may dye their hair or wear some form of head covering in order to hide the color, but that's generally rare.