Silver dapple is not grey.
Grey horses start out as almost any color - often bay or chestnut or black, and start getting more and more and lighter hairs, as they get older. They often 'grey' to a 'rose' color, then to a really noticeably grey color...and then that grey tone starts getting lighter and lighter as they age.
Silver dapple is a special modifier gene, that can sit on top of several different coat colors, and modify that base color, diluting it to look like - well - the pictures you see.
Sort of a sepia color with light and dark areas ('dapples') - it can be blacker or browner than the above examples too, but is not reddish, yellowish - it's always that very sepia brown with no yellow or red highlights. And the mane and tail are lighter than the body color - sometimes much lighter.
The silver dapple gene is found in Welsh ponies, Shetland Ponies, Dutch Warmbloods, and occasionally, in some crosses involving those breeds.
It can crop up in other breeds as well. It's a mutation, but a delightful one.
Unlike most color differences, the distinction between silver dapple and grey is quite useful, because grey horses tend to get skin cancer - melanoma - fully 80% or more grey horses get melanomas.
And while it isn't as serious as melanoma in humans, it does occasionally actually cause trouble, even serious trouble - so people like to be informed and make an informed choice - if the horse is grey, or actually some other color.
