I've always wonder this.

Why do greys, who start off super dark, end up nearly white (i know they are not white, but they look it)??

A 3 y/o at my barn .. There is a picture of him as a yearling.. He is a solid bay/black (l can not really tell, its not a great picture) and now, two years later, he is a dark dapple grey.
Also, my pony is a medium grey with a super dark grey mane/tail. She is lightened up ALOT and her mane is starting to come in white..

WHY??
I am not talking about sun bleaching.
I am talking about through the years, why do they get lighter?
As a baby, they are dark grey/black. By the time they are 15+ they are super light grey.

Sun exposure could lighten their coat color. Or, that was just his baby coat, he is growing out of it.

bc its normal just like humans our hair gets lighter and lighter unless we like shave or something its just normal for greys to do that my first poney daisey was like that and l was so happy when she got lighter

sun exposer
loosing his coat
stuff like that can lighten a coat
This black horse l ride starts of extremely black in the summer but then mid summer turnes bay or a rich brown color
his color is just fading

Here is what l found:

A gray foal may be born any color. However, bay, chestnut, or black base colors r most often seen. As the horse matures, white hairs begin to replace the base or birth color. Usually white hairs r first seen by the muzzle, eyes & flanks, occasionally at birth, & usually by the age of one year. Over time, white hairs replace the birth color & the horse changes slowly to either a rose gray, salt & pepper (or iron gray), or dapple gray. As the horse gets older, the coat continues to lightens further to a pure white or fleabitten gray hair coat. Thus, the many variations of gray coloring in horses r simply intermediate steps that a young horse takes while graying out from a birth color to a hair coat that is completely ''white.''

Different breeds, & individuals within each breed, take differing amounts of time to gray out. Graying therefore cannot be used to approximate the age of a horse except in the broadest of terms: a very young horse will never have a white coat (unless it is a true white horse), while a horse in its teens usually is completely grayed out. One must also be careful not to confuse the small amount of gray hairs that may appear on some older horses in their late teens or twenties, which do not reflect the gray gene & never cause a complete graying of the horse.

It is the gray gene that causes it. It is like us having genes that make us gray earlier. Their gene makes the gray hairs be replaced by white hairs.

the sun

Remember that 26 year old singer on American Idol with the grey hair? It is basically the same thing. The horses have a gene that causes their hair to grey very quickly.

Strangely enough, grey is not a horse colour. It is a gene that modifies their colour, & makes their hair change - similiar to how some people grey early.
Greys do not have to start off super dark. In fact, a grey horse can be born with any base coat, so they can be born black, but they also can be born palomino, roan, sorrel, or anything else. The grey modifier gene quickly kicks in, often within a few months their hair coat begins to change. Different individuals change at different rates, some will become almost pure white within a few years, others can take a much longer time to become white.
You r right, it is not sunbleaching that causes this. It is the gene modifier that causes their hair to lose the natural pigment.
By the way, scientists now think that all greys share a common ancestor, & that it began as a mutation. Nowdays u cannot get a grey horse without at least one grey parent. And u can have homozygous grey horses (with two grey genes) which will pass on the colour grey to each of their offspring.
Hope that helps.

That is what the grey gene does. As the horse ages the hairs come in with less and less pigment. Eventually they will turn almost white, but will often develop little color spots called flea bites when they get older. A horse that develops 'flea bites' will usually get more and more of them as they age.