"silver" is a modifier, not an actual color. The silver gene acts on black to lighten the color to varying degrees. Some silver blacks will have a very light "dapple grey" body color--such as maryann's 4 year old photo above--while others will be a dark chocolate color, like Ice Man below:
This was Ice Man at the age of 3 months:
This is Silverado at the age of 3 months:
At birth he looked palomino (golden) but by the time he was a month old he'd faded to the color above.
This is Silverado at 1 year:
He is a silver black, but a very light one. At maturity he is a little bit darker, especially in spring when he first sheds out, then over summer he lightens up again.
The filly I posted earlier: (she did not inherit the grey gene by the way)
became this color as she got a little older:
And then became this as a yearling (neck shows her real color--she still has a bit of winter fuzz in places!):
As you can see silver blacks come in many shades, and can have major color changes between foaling and maturity. Why are they silver blacks and not chocolate palominos? Because genetically they are black horses with the silver gene. Some may look like chocolate palominos as foals, but they grow up to be obvious silver blacks. Some will look like chocolate palominos even at maturity. I would point out, though, that many so called chocolate palominos are in reality silver blacks, and not palomino at all. To be palomino a horse must be red based with a cream gene. If all "chocolate palominos" were DNA tested I think there'd be a few surprised owners when the test came back showing their palomino was black based!