In real world™ marketing at major MNCs, you make substantive choices backed by facts and data.
That is not always the case.
Black and silver (and gold in some cultures) are known to be strongly associated with luxury, exclusivity, and upscale goods. There are psychological studies behind this. Can you argue in favor of red or white, especially for an underdog in need of global attention? Sure, but you don't give "umm, car pics are going to be not-black" as an answer to a question about Cadillac's "Americanness."
Uwe/Cadillac is focusing on a specific type of image. Certain colors convert a certain message.
You can absolutely make a case for colors and its portrayal in corporate messaging.
"Cadillac is about American luxury!"
'What is American luxury?'
Reminds me of when Buick's slogan was "The Spirit of American Style" featuring Harley Earl's ghost in TV ads. No one knew what the hell "American style" meant, the message didn't stick, and now Buick's most competent offering is an Opel. I'm all in favor of using nationality to define a brand as Jaguar is distinctly British, Volvo is very Swedish, Lexus is proudly Japanese, and Ferrari is very Italian, but if you can't provide a pithy answer to a basic question about how that nationality is interpreted in the context of your product, you need to find another direction.
The problem here is that there is no such thing as "American Luxury."
I've made this point over and over here for years. American luxury is defined by other more global/European standards. There is no distinct and unique version of luxury. And even if there were, it's not seen or perceived as equivalent or greater than the European standard.
When you say "<Insert country here> luxury," it's going to project certain connotations. There is nothing that says anything about American luxury.
So Uwe's challenge is to determine that that means for Cadillac going forward and then play off that in all marketing and branding aspects.
Like I said months ago. Uwe was in charge of having to sell and marketing $1,000 ballpoint pens. Selling an American luxury car should be a cake walk.