Ok, have opened mine and the STI parts are NOT BLACK. They are more of a really dark satin gunmetal color. The sheen matches the stock silver plastic in terms of gloss with a bit more texture.
They don't appear to be simply painted either as the top coating didn't scratch off. I'f I had to guess I'd say they spray the metallic/color/texture into the existing mold of the part and then inject the liquid abs fusing them together.