How can cat hairs with one color on the tip and another at the base?

Factual Questions
1

I have a gray tabby. If I part some fur, it’s white at the base, gray at the tips.

I can imagine a scenario where a hair follicle might apply pigment to a new hair, then stop, so the bottom looks white. Then the hair eventually falls out, the follicle gets re-energized and the replacement hair gets pigment. But if that were the case, wouldn’t I also be seeing new replacement hairs coming in gray?

Imgur

2

Cats don’t just have one type of hair,

Cats have four types of hair. They include:

  • The coarse and shiny guard hairs of the outer coat are the longest. They deter dirt and moisture. Guard hairs display the cat’s basic color and pattern the strongest.
  • The thick and bristly awn hairs of the middle coat are shorter than guard hairs. Awn hairs are just beneath the guard hairs and protect the undercoat. Awn hairs carry less pigment for color and pattern than guard hairs, but more pigment than the undercoat,
  • The soft and dense down hairs of the undercoat are the shortest. They insulate and help regulate body temperature. If not groomed properly, the undercoat is prone to matting, which can be uncomfortable and even painful.
  • The sparse and baby-fine vellus hairs are usually found in hairless breeds.
    https://kittencoalition.org/hair-the-long-and-short-of-it/
3

It’s not the same strands of fur. Cats have different coat layers. The fuzzy white stuff is your cat’s down layer. The colorful hairs are the awn layer and the ones that stick out beyond the awn when it’s frightened are the guard hair layer, also colored.

4

This is true, but you are missing the explanation of how come individual hairs on a tabby cat have one color on the tip and another at the base.

Such agouti-colored hairs are the result of different forms of melanin produced during the growth of the strand.

5

True, I had a bengal cat that had gold tipped hair and always wondered how that was possible. Looking forward to an answer.

6

The black bands are eumelanin (“true” melanin) and the gold bands are phaeomelanin (“grey” melanin). Production is regulated by the MC1R receptor on melanin-producing cells, which is activated by melanocyte-stimulating hormone and antagonized by agouti-signalling protein which competes with it.

7

OK, so now we know that there are multiple types of hairs, and how one hair can have multiple colors.

On people, your hair grows to a given length, then stops growing. After a while it falls out, and a new hair grows in from the same follicle. I would assume that cat hairs work the same way. If so, why don’t we need new pigmented guard hairs coming in among the undercoat hairs?