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I seek a realistic method, either by genetic change or other scientific method that doesn't require magic or future tech, to obtain naturally occuring two tone hair for a race of humanoids.

My idea is simple, as the hair grows in length, X happens that causes a natural change in color. Basically the higher the "Age" of the hair, the more it changes, either by exposure to air or what have you.

The issue is, I can't solve for X.

I'm already using another race that has cyanophores in their hair naturally from consuming creatures that contain them on their planet over time. Their effect is simply when their hair gets wet it slowly changes to a bright blue.

But for two tone hair? I'm stumped.

Is such a thing possible?

Please keep in mind their home planet doesn't need to be just like earth, I will adjust it to meet this possible requirement.

Also: I seek to explore the possibilities of how the hair could change color quickly enough to make the switch from say, brown to blonde occur quickly enough to allow the gradient change to only appear in around half an inch of the hair itself.

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There is another example in nature that hasn't been mentioned yet, "Agouti banding". My tabby cat's fur has bands of color like this, with grey then beige then a dark band and some have light tips.

enter image description here

Other animals also have this type of coloring (rabbits, dogs, horses and mice are also mentioned in the wikipedia link).

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  • $\begingroup$ When I was young, I thought of my hair as black, but that wasn't really true. A close look at my hair revealed that it was a mixture of black and mahogany, an extremely dark red. Now I'm gray, but it you look closely, my hair is a mixture of white and black. I think what happened was that the follicles that were putting out the mahogany stuff turned white, and the black follicles are just hanging in there. $\endgroup$
    – Howard Miller
    Commented Oct 16, 2015 at 19:06
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Human hair naturally bleaches in UV light from the sun; "beach-blonde" is a desirable change from mid-brown at the roots through a gradient to blonde; coupled with a deep tan, the look is someone who has enough leisure time to be outside playing on the beach all day. It's a switch from older historical preferences in many cultures for very pale skin, indicating someone who is wealthy enough to not have to work outdoors (now that most employment is indoors and sunlight exposure itself is the luxury, the preference is largely reversed). But I digress.

Given that this basic property holds for your aliens' hair, all you need is a base color that doesn't bleach out when the melanin (or whatever) does, and voila, you have hair that bleaches blue (or red or green) over time.

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It already happens a little bit on earth - it's called sun bleaching.

Have the hair created with two pigments, one of those pigments is sensitive to light and gradually gets damaged by it.

Now hair near the roots will be one colour, but then it will transition to the other colour as the first pigment is destroyed by sunlight.

This could have some interesting cultural effects as well, covering your hair and protecting it from the sun would keep it single colour.

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The hair could contain a combination of chemical substances that changes colour after a given time. If the time needed for that process is long enough to allow the hair to significantly grow, but smaller than the life time of the hair (say, about half as long), then you get two-tone hair.

See Wikipedia for such chemical reactions.

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The mechanism already exists on earth, and is seen in the different winter coats of Arctic and sub-Arctic mammals such as Arctic foxes, stoats and rabbits and hares. Responding either to shortened days and/or dropping temperatures, the animals stop producing pigment in their brown fur, and it grows out white.

Similarly, you would have either a one-pigment or a two-pigment system. A one-pigment system would operate like earth animals, with a base color for the hair and an overriding pigment which is produced either only in early life or in later life. A two-pigment system would presumably occur with a relatively neutral base color for the hair, and one pigment produced early in life, while the other is produced later.

And for what it's worth, a restrained version of your desired change can occur in people. In my family, several males were redheads as children, then turned brown at puberty, then white when older.

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Sunbleaching or an aerosol in the environment could cause the color change. Bleaching by the sun on earth breaks down the pigments causing the item to go white. However, a chemical reaction with an environmental aerosol would allow the hair follicle to turn to a color other than white. Depending on the interplay between reaction rate, aerosol availability, and follicle growth, the follicle may change color closer or farther from the root.

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