Eames lounge Herman Miller black shells.  

Here's a picture.
picture

Another
Another picture. Wood grain more visible.

Normally I would suggest...
Normally I would suggest it's someone's unfortunate d.i.y idea, or maybe a special order from Herman Miller.
Didn't Vitra do a version all in black way back in the 70's?

According to the previous...
According to the previous and first owner who bought it back in the seventies, I believe 1972, this is an original version. It hasn't been coloured black by the owner. Since the shells are black on the inside too, I think it came this way from Miller. I've seen Vitra-editions all black but they are lacquered including the sides of the shells and no woodgrain is visible. This Miller-version hasn't been painted, it's like coloured in the wood leaving the grain visible. I think rather nice in an interior with black and chrome but hey, that's personal opinion.

I've seen black before
Both as production pieces by Herman Miller and Vitra and as a modified (or painted after the fact) chair presumably painted to conceal damage or a repair. Yours has the H.M. base rather than the Vitra base. And I believe you are correct that the Vitra black chair is totally black with no exposed edge.
I doubt the wood is rosewood as the grain is too pronounced. Rosewood is much smoother and it would be a shame to stain or paint rosewood. Looks like perhaps teak or ash. H.M. did produce 670/671 in teak, walnut and other woods as a special order back in the day.

I own one.
Also early seventies vintage with black "aniline-dyed" ash veneered panels. Looks like paint to me, but the ash grain is still quite visible. Edges on mine are black. Came with brown cushions. I rather like the reverse scheme. Everybody has rosewood/black.

.
I think that the black leather paired with a black shell looks divine. Herman Miller should re-introduce this combo. ..or just re-introduce the black shell with any color leather. Why not??
Just a thought.,,carry on.

Bunshaft had one
Gordon Bunshaft (architect at SOM) had one in his house on Long Island. Chair is all black, edges and leather are black too. See photo at p. 182 of monograph by Carol Herselle Krinsky (MIT Press, 1988).

Original versus repaired
That is the clue when looking for all black. Before buying this one, I have seen a few. And yes, when damaged and repaired an easy way to hide things, is painting it black. Here in Europe lots of dealers of antiques (is dead commercially speaking)jump to vintage. They don't care about design just making money. I examined mine a lot before buying and I believe it's legit. Here's some more pics for anyone who like me think black is divine 🙂

More black shells!
I also have the same combo. Mine have a black rectangular label but are slightly unusual. They read "Herman Miller 1 " with a registered mark also.
I was also told that they were bought originally in the early seventies either in Glasgow or London. Where are yours from?
I think they are magnificent and very unusual. The unstained edges make all the difference compared to the new Vitra one which is now available.
They have proved to be unbelievably hard to find out any info and through hours of browsing i have found another lucky owner. Hopefully you still check the posts as i would like to hear from you.
Regards
DaveW
Edinburgh