Wallace, the W111 and W112 coupe` and cabriolets did have colored entrance rail sill coverings throughout the production run, but as the years went on they did drop a color or two. The last handful of 250 (Approximately the last 100) and all 280 models in particular were the recipients of this. For your car with the cognac interior the entrance rail sill covering would have been "dunkelbraun", or dark brown. (see pictures below) As this material ages it darkens, and you wouldn't be the first one to mistake what was once dark brown for black......because it really looks black when it gets some age on it. I feel that black was the best choice considering dark brown isn't available, and black seems to tie in with the cognac leather better than creme`.
However, for the 280 models the section covering the "Riffelgummi" changed the section description to "Belag Einstieg aussen", or "bottom entry, outside". I can only speculate that they did this because the heel pad and the anti scuff mat to the right of the foot feed always seemed to be the same color. Yet, I've seen just the opposite on several models. It wasn't uncommon for Mercedes to use a different color during production if they had run out of a certain color. Sadly, this would not have been noted anywhere.
For the late 250 and all of the 280 models there were a total of 4 colors used for the entrance rail sill coverings. Dark brown, dark blue, dark grey, and beige. The blue and brown fool even the best of us into making us think they were black all because they darken with age. They were really dark shades of brown and blue to start with, so it doesn't take much. Interestingly, the beige covering was used only on cars with interior trim code 251 Beige.
Now, with the very late W111 3.5 models (003455 onward) a two more colors were introduced, but two were removed. So only 4 colors were still available. The new colors were Bright beige and blue. These replaced beige and dark blue. Though, the majority of interior colors utilized the dark grey color. Where the different colors came in seemed to be for interior trim codes that specified a two two tone interior. For example, interior trim code 256 (parchment) came with dark brown entrance rail coverings and dark brown carpeting, and interior trim code 255 (also parchment) came with blue entrance rail coverings and dark blue carpeting. I imagine this was done to be more appealing to the eye when the door was opened.....they didn't want us to see a dark gray entrance rail covering with dark blue carpeting.
Conversely, for the 220 and most 300 models there were a total of 5 colors used for the entrance rail sill coverings. Medium grey, Creme`, Blue Grey, Beige, and Olive Green.
For the W128......I'd have to find my early interior appointments book to answer this part of your post with any certainty. Given that a lot of the very late W128 attributes carried over to the very early W111 and W112 coupe` and cabriolet models I can only assume that black or grey would be correct, as that's what was usually used with red interiors. When I get home I can look this information up for you. Just keep after me so I won't forget!
