A purist would say check the data card, Phil. And I'd say if you have an exceptionally rare original black 280SL, you're almost duty bound to respect what the data card says. I've never seen an original black w/cognac.
Any of you who were around at the end of the W113 in 1971 will recall that the vast, vast majority of U.S. 280SLs -- I'll wager 85% -- delivered with whitewalls, even the ones with the new and seldom-seen alloy wheels. Almost all of us eventually traded in our short-lived, wider-striped 185 Continentals and Phoenix's [Phoenices?] for thin-striped 195 Michelin X's, which looked demonstrably better while still retaining the whitewall esthetic; simply a reflection of the times. Remember, too, that special curb ridge on the factory tires was specified by Mercedes, precisely to protect the whitewall. Whitewalls were neither an afterthought nor unrespected in Stuttgart.
The end of the whitewall era came with open alloy wheels and a European style that most Americans wouldn't embrace for years. But for Mercedes in America, that started with the R107, not the W113. I briefly tried blackwalls, but switched back because it just didn't look like the car Mercedes built for me
(And, Cees, I have that black-on-black whitewall model too -- it's a beauty.)
'71 Tobacco/Cognac 280 SL #22375