How does the gray color work?

So...I'm a little ignorant about gray horses.
I had a flea bitten gray arab mare who I got at an auction who was very very light. I later found out online she was registered..and at one point had a star and snip...but she was so faded you couldn't see them any more at that point. A 4-H leader told me that grays lighten up alot as they age.
So...would that mean that all "gray" horses start out with dappling dark color as youngsters, and get flea bitten as they age? And fade to white in old age? By what age are face markings TYPICALLY no longer visible?

I just bought a supposedly 14 year old feedlot horse who I haven't met yet, and from the pic I saw he's got a dark mane and tail but lighter body.
The AMAZINGLY awesome nice lady who runs tge rescue went to get him and says he has a very distinctive blaze. She also says he has some dappling. I'm wondering...if he's still got some dappling, and still has a distinctive blaze...does it sound like he's probably younger than 14?
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Gray horses will all lighten in different times. I have known some gray horses that were almost completely white by the time they were 7 or 8 and I have known others who were still a dark steel gray with dapples up into their late teens.

Typically, a gray horse will be born one color (non-gray) and that color will be overtaken by the gray modifier. Also, not all gray horses will get fleabites. Some just fade out to white with no other color mixed in. My mustang was papered as a buckskin when he was captured as a yearling but now, he's as gray as he can be. He will end up having a few fleabites but since they are yellow, they are hard to see. The fleabites that a horse gets are also usually the color that they were born. I don't know what causes them.

Gray horse with no fleabites


Horse that is fleabitten to the extreme


Then there are others who are never dappled at all.

But, they all do fade out closer to white as they age, some just white out faster than others.

Grey horses go through phases as they lighten up. They are born a solid color, and can either have a white mane and tail, or dark mane and tail. Usually with a dark mane and tail they take longer to lighten up, and very rarely you get a grey horse that is born light, and by the first shedding of the foal coat is completely grey. My mare will most likely always have a black mane, and black and white tail (her mom still at 12 years old has a darker mane and tail), but a lot of grey horses end up completely greying out, including the mane and tail. As smorbs said, not all horses end up getting flea bites, the horse actually has to have the gene modifier for it, and from what I've read, if the grey parent(s) isn't flea bitten, then the baby won't end up being flea bitten. Also, some horses don't ever grey out completely, and instead retain an almost varnished appearance with some parts staying darker. Grey is definitely a unique color to study.

Grey is a modifier on top of the horses color. So a grey horse starts out whatever color the horse would be if he didn't have grey. Bay, chestnut, palomino, you name it. Greys are often born an adult shade... meaning, a bay with grey will be born looking like a bay, where a bay without grey is born brown on body and light colored legs. This isn't always the case though.

Grey effects the color producing vells, melanocytes. It causes hyperproduction at first, so at first a horse darkens. Because of this, once a horse starts to grey, its impossible to determine the base color, as even a palomino will look like its black greying out. Often, not always, they move to a dapple grey phase. From there they continue to lighten throughout life, but how fast is an individual horse thing. Some get fleabites, some don't.

Theory is homozygous greys grey out faster, and heterozygous greys are the ones that fleabite. Even this theory says usually, not always ;)

Greys change at different rates but all will get lighter as they age, some get flea bites, some don't. Here is 2 horses owned by my friend, both are 7-8 years old

Here's a site that explains it really basically and it's accurate and easy to understand.

Horse Color Genetics that YOU can understand* Genetics is a scientific theory