sounds like either copper chimney pots you are referring to or creosote/soot etched/stained 304/316 stainless steel. a light creosote stain will produce the colors that you are referring to; it is somewhat common.

Thanks berlin, would this coloration of the stainless be a by-product of normal use, heat cycles, exposure, etc?

A shiny stainless would stand-out loudly. How durable are the black finishes? They appear to look like the old flat stove paints. Do they require "touch-up" to keep a uniform look?