That's the way the factory did it on 68-70 Charger dashes where the instrument surrounds are "chrome" and the rest of the panel is black.
Thet just painted black over the "chrome". I had a NOS 69 Charger panel where the black paint had flaked off some small areas and Chrome was showing through, fixed it with a spray can. I'm pretty sure that's how they did it on all the plastic dash parts.