A silver finish will reflect heat and keep camera internals and film cooler in hot conditions. The "silver" finish I believe is a hard chrome and also wears better. The black finish is not as durable, typically. As a result, the black will wear and show brassing more rapidly than a silver finished camera. Ironically, you pay more for the black camera but the resale will go down faster if it shows brassing. I am speaking from my experience of using older Nikon SLR's. There may be many exceptions to this.
I have two Nikkormat's and I use the black one more but the siver one is broken
They are of the same general age and the silver one looks better because of the brassing. Of course brassing has nothing to do with image quality.