Trunk trim is anodized aluminum. As it ages, the anodizing gets dull. Oven cleaner is often used to strip it off. Then you can buff the aluminum, but it won't stay shiny unless you keep it waxed, or clearcoat it.
The flat finish areas are silver argent paint (very close to Krylon dull aluminum).
I'm sure there are threads that go into greater detail if you search.