The implication being that it would be OK to re-color a Picasso print, but not a Picasso painting ?
Fortunately Dr. Simeone offers the appropriate prescriptions: Coachbuilt Press | The Stewardship of Historically Important Automobiles
But in this particular case, I think a tasteful and thoughtfully-chosen variation led to a more attractive car, that brought more money, that will encourage the preservation and appropriate restoration of more of its type. All good.
But that stray pipe wrench depicted in the tool kit still makes me cringe . . .
If we're discussion his late work, as far as I'm concerned you can use most Picasso prints to wrap fish. But that's a different argument.
I'm not really going to get into an extended discussion on this question, but I deal professionally with preservation, restoration, and adaptive re-use of historic buildings; objects whose preservation issues and principles are far better developed than those for automobiles. I tend to favor originality in nearly all instances. But circumstances and context always factors into any serious discussion that doesn't reduce the question to religious fundamentalism; Paolo's "Taliban" comment wasn't far from the mark.
As for Fred Simeone, someone whose work I greatly esteem and with whom I've discussed these issues, he does indeed address this question. But if you read his excellent book, he doesn't suggest that a standard production Flaminia PF Coupé, with no special history, would rise to the level of "historical significance", thereby warranting strict conservation, or at least demanding perfectly correct original standard--particularly on a reversible modification like paint color (at least once the original paint is beyond conservation).
So, yes--standard series production cars are indeed different than one-off works of art. And as you correctly point out, we're discussing a particular situation in which it involves a "tasteful and thoughtfully-chosen" color change, and in which the results themselves may well help justify proper restorations of PF Coupés. Given all that, it's fine to argue questions of taste, but let's keep morality of a discussion of this particular example.