I don't have a problem with black optics on a stainless rifle. I think it looks just fine, which is good since silver(ish) finished scopes can be much harder to find and more expensive. Also, as mentioned, the "silver" or "stainless" finish on the scope can run anywhere from a dark greyish matte stainless to nickel to matte aluminum, and they seldom match the rifle. Black is black for scopes. The only difference is matte or gloss, but it's still black.

Here are a my stainless/black rifle combos...

My Remington M-700 with Zeiss Conquest matte black scope in stainless rings (though I wish I'd have gone with black rings now, because they don't perfectly match the receiver):