I can't speak definitively for the Calais (though I assume it's the same as the SS), but the black parts on my car are definitely painted such - you can see the overspray if you know where to look

I'd take a comparison photo for you, but my car is having it's gearbox dissected at the moment
I can understand on an imperfect finish would bother you (they bother me too!). I'm probably stating the obvious, but I'd suggest testing whatever solvent you intend to use on the underside of the centre console (or another non-visible area) to make sure it's not going to melt the plastic. Next I'd test it on the T/C button to test if it's going to cause any undesired effects on the lettering (assuming of course you intend to treat the entire console, not just the radio?) because that way, the worst case scenario is a new $20 button from Holden.
Anywho, best of luck, lots of photos please! (but you knew that already didn't you?

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