Not sure what Viper he is talking about, but the GTS '99 is a black interior just like the other standards, I haven't checked the '03 Roadster yet.
Understand this, the standard car interior are basically silhouettes of the actual car interior. So far I checked quite a few cars and the interiors actually reflect what the car looks like from inside. Check each and every car, those interiors are only generic among the same model type (miatas, R34 Skylines and such). Other than those, every car has it's interior just blacked out which I prefer to those hyper detailed Premium as it's easier to focus on the viewpoint.
Anyway those interiors are pretty nifty, I also noticed that when your car is pretty powerful you get this judder and shake at increasingly high speeds. Wish there was an option to black out the premium car's interior, that would help me focus instead of getting lost in the details.
Now if PD would allow the body of the car to show in car standard view would be a little more immersive. It's just weird to look back and not see my giant spoiler. Thought PD basically positioned the camera in the drivers' position as they did with the open top cars, I'm pretty sure they did something like that so they might as well turn on the exterior as well. Just my 2 cents.