When my daughter was about 10 months old, her head was shaved as is the custom with infants in India. She started life with black hair which remained entirely black up until the shave. After her one shave it all grew right back light brown, all at once.
What’s the explanation?
She’s a reverse siamese cat. Coat color in siameses is temperature dependent, with the darker color growing on the cooler parts of the body. When you shave a siamese cat on the tummy, the fur grows back dark because the shaved area is colder than with the fur on.
So clearly, your daughter is a revese siamese cat.
Infant hair colour is a funny old business; I was born with thick, jet black hair that lasted about eight months, then it all fell out (apparently in handfuls) and regrew in very pale blond (almost white - think Midwich Cuckoos). The colour faded through mousy brown in my teens and now, in my late thirties, it’s almost black again (what is left of it).
My two children appear to be following exactly the same pattern; born with very dark hair that later fell out, leaving them bald and regrowing with pale blond/blonde.
It may be that your child is doing something similar and you just happened to shave her head at the point when it was about to change naturally.
Each individual hair only grows out so far then stops, and falls out. Then a new one grows in to take it’s place. If you daughter’s hair color was undergoing a natural change, and all new hairs had started growing in lighter, you would have noticed it only gradually because all the old, nongrowing dark hairs were still there and hadn’t fallen out yet. Then by shaving her head you would see this change all at once since all the dark hairs that stopped growing are gone.
Just a hypothesis.
Mangetout and CookingWithGas, that’s about the same theory I was thinking up too. I started losing hair in clumps as a result of recent chemo. Fortunately I was able to halt the sudden loss while I still had hair, the chemo is all done, and I expect regrowth. But I noticed once my dark hair started falling, I started to see some more gray revealed. I guess according to this theory it had been there all along, but unseen.
Hoping for the best for you.
I’m all better now, thanks. 
Johanna - me too! Finished rads on Friday, February 10.
Whew! It’s been a helluva journey.
Johanna - I’m curious about the custom of shaving infant’s hair in India. I’d never heard of it, not that I am very knowledgeable about customs in India. Can you tell me more about it? Done on a certain date? For what reasons? Always done? A celebration? A practical matter? Just curious.
Congratulations, **straykat[b/]! I’m so happy for you!
CBCD, as far as I can tell all the religions in India practice shaving kids’ heads, and each gives their own explanation for it. It’s done in other countries too. I think the idea is to promote better hair growth, but sometimes they make a ritual of it, weigh the hair clippings from baby’s first haircut, and donate the value of that much weight of silver to charity. And have a party. Things in life are ritualized so people can get together, I guess. Part of being social animals.
Is it done to all infants, or is it a girl vs boy thing? Is it always at 10 months? Is there some significance to the age?
The ritual is called “mundan” among Hindus, and AFAIK the age of the child might vary depending on the sect or whatever. Shaving the head is considered an act of religious humility and dedication and is also practiced at other times, e.g., on the death of a parent or spouse.
Coolness. Thanks for the info!