Why do Americans call hair that turns white "gray hair" not "white hair?" [closed]

Gray (often spelled as grey in the UK) is an optical illusion. In actual fact the strands of hair which are always white, only appear gray because they are mixed with the remaining, naturally dark coloured hair. This explains why many people, not only Americans, say they are going gray. Some people never turn completely white haired because some hairs never lose their melanin.

As people age, meanocytes slow down their production of melanin or stop working altogether, which results in a lack of pigment. Hair that lacks melanin looks white, while a mixture of pigmented and unpigmented hair results in a gray appearance.

_{Sources: Anatomy and Physiology for Health Professionals and Encyclopedia of Hair: A Cultural History}

I'm American, and it would never occur to me to call it "white hair," no matter how close to #FFFFFF the color became. Once the hair loses its original color, it's turned grey, and, unless you color it, it stays "grey," even when it looks white. Why? I don't know, but there's been a lot of hullaboo about 50 shades of grey lately; maybe the clue lies therein.

As for the Ngram that's caused so much ruckus, that's easily explained by clicking on the links beneath the Ngram, and letting Google books dig up and display some sample usages. Most of the examples of "white hair" seemed to be talking from a very scientific point of view, where factual accuracy is presumbly paramount, or else talking about something else entirely:

However, the tryptophan levels are highest in grey and white hair, showing that tryptophan accumulates among hair fibres with age. Therefore, there is a correlation between tryptophan content and hair pigmentation.

The investigators administered chronic doses of radiolabeled chloropromazine to rabbits and determined the percentage of drug incorporated into black and white hair by measuring radioactivity of hair samples...

This one comes from a book on raising and showing guinea pigs:

Roan is the even distribution of white hair with any other colored hair.

and here's a reference where "white hair" refers to "hair on white people":

Craig also notes that “the dominant interpretation of African American male and female hair straightening has been that it expressed identification with a white hair aesthetic.”

So, unsurprisingly, we get a lot of Ngram hits when we look for "white hair", but they don't help us determine what color aging women are thinking of when they buy their first box of hair color, or what word men would use to describe their own salt-and-pepper hair.

On the other hand, many of the hits on search for the "grey hair" refer to hair that has lost its original color due to aging:

In Greek mythology, the power of Medea, the sorceress who fell in love with Jason, leader of the Argonauts, depended on her skill as a perfumer and her ability to use vegetable dye to turn grey hair black.

Traditionally, grey hair has been a sign of advancing age. People made a fuss about Barbara Bush's grey hair on the grounds that it made her look more like the President's mother than his wife.

"So, the more you worry about your grey hair the more grey hair you have, and the more grey hair you have the more you worry about it."

Here's one that addresses Mari-Lou's remarks:

Later in life grey hair develops. The grey colour is usually a result of a mix of coloured hairs and white (non-pigmented) hairs, although sometimes individual 'grey' hairs with reduced pigmentation are found.

I'd conclude that the Ngram supports the notion that most Americans call it grey hair, although you must do a little detective work, and not form a conclusion just by looking at the two lines.

I'm not going to lose any sleep over the fact that I've been (incorrectly?) calling white hair "grey" – after all, we often use imprecise terms when referring to color. Perhaps the sky is blue, the ocean is blue, and the American flag is red, white, and blue, but those blues aren't all the same color. We talk about "black people" and "white people" when really their skintones are more like a rich brown or a pale peach. Many yellow delicious apples I've eaten look more green than yellow. We speak of being red-faced when we are embarrassed and our skin blushes pink. We order red wine that looks closer to byzantium than red, and white wine that looks more yellow than white.

The Book of Proverbs says:

The glory of young men is their strength, gray hair the splendor of the old.

I'm old enough to have lost a good bit of my strength, but young enough that I still have my original hair color. No strength, and no splendor. Maybe that's why men my age are so prone to midlife crises.

Perhaps in recent history not many people lived to have white hair but many lived to have grey (white + original color) hair? I've seen lots of people with grey hair but not all that many with white, so perhaps its a reflection that white-haired elders tend to remain isolated and out of the public eye while many grey-haired people remain in the workforce and thus are seen? Also, bluehair is a derogatory term I've heard used on enough occasions that I remember it.

If you're literally talking about the color of a given person's hair (as opposed to a generalization about older people), I think people use grey or white depending on the actual color. (In other words, I'm trying to say that the "gray-hair" you've heard seems to me to be a generalized and somewhat derogatory term rather than the term that's always used for gray and/or white hair, which is what your question seems to imply.)