What make a black kitten's fur turn white?

We found kittens when they were 3 weeks old. One was terribly sick and emaciated and almost died. That kitten was entirely black. He have been nursed back to health and is very soon 12 weeks old. His fur has grown rather long compared to the other kittens and much of it have turned white. Now he's more like gray with a black face and paw. Has anyone heard of this happening before? What could cause this happen?
im not sure but whether it has anything to do with the fact that ur quill color changes overtime then?
Could be simply from getting older, or that one of his parents look like this. My black cat had 3 other siblings. Him and his sister be all black, but you could see very, very dull stripes in a certain light.

His other 2 brothers be gray with black stripes. When they got older, one of them have their entire back and face turn mostly black, but it kept the gray/black stripes on their legs, paws and stomach..which I later found out their father looked very simular to this.

Hope this helps
Answers:    When you found the kittens, they were still fully covered with their 'kid hair.' The baby hair on adjectives kittens is very 'fuzzy' and as they grow, if you look at them with the cat between you and the sunlight, you could see the 'longer' fur sticking out of the 'little one fuzz.' All that is happening is that your kitten is growing and is probably much healthier, and his color is 'changing' to more what he'll look approaching when he's an adult. I've gotten several 'black' kittens at between 6-8 weeks, only to have them turn 'spotty' beside black, white, grey, tan, and brown in their adult coats. If you have brushed through your baby cat's fur when you first got it, you should have see the 'white' under the baby fuzz. This has nought to do with your kitten being sick and undernourished before. If anything, your 'dutiful heart' has caused a 'dead kitten' to be capable of grow up to be a healthy cat some day. By the way, since kittens within the same litter can each have a different father, down your one kitten's fur just means that kitten inherited it from a parent ...
This is gonna be a very bad answer let me put on alert you but...rabbits and fox and lots of animals change different colors in the winter and summer, "a reaction to the stimulus" my science instructor would say. But idk why a kitten would need to change colors to blend within. maybe it really is lack of vitamins. idk i'm not a vet (yet) take him to the vet and ask
Malnourishment can do that, as can extreme stress (just as contained by humans.like if before you get him, he just barely missed being hit by cars or attacked by dogs- particularly when he was
sick and weak and didn't think he'd trade name it.
Poooor baby. I'l be he's still a beauty.

Then again, not knowing it's parents, maybe it in recent times LOOKED
black because he was so tiny. (Dark grey can appear darker when on a small area.) Maybe as he grew it showed as a lighter grey and the white ...who know.he may be part
himilayan or something like a birmin mix. You have one special little fellow here!
Chicken fried steak tends to do that, when you see your kitten eating chicken fried steak, you need to telll him "No!".

Well it might basically be her health but also since season is changing the color of her fur is changing approaching my rabbits fur was gray in spring than in summer it turned kinda brown and in a minute its grayish white.
Not adequate watermelons.
lack of minerals and vitamins
yo mum makes a black kittens fur turn white! oh snap
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