Welcome to the forum. That's a beautiful aquisition you've got there.
Regarding the color of old Hard Rubber, I have Hard Rubber clarinets that are over 100 years old and look nearly brand new, and black as coal. I also have samples in various shades of green and greyish-brown, as you suggest.
Hard rubber is essentially "photographic", meaning it quite literally retains the impression of light's influence. A perfect example of this is a hard rubber clarinet of mine which likely sat in a display window or an illuminated case for many uears without moving, and the side exposed to light is greenish brown, while the unexposed side is jet black. Further, the obstruction of keywork shielded certain areas of the clarinet, and those areas that were shielded are not only much darker, but very approximately show the keywork shapes on the rubber, itself, which I find rather fascinating, and admittedly--amusing.
If hard rubber is kept out of the sunlight and its exposure to fluorescent light is limited, it is not prone to fading, so judging composition by lack of fading is, at best, a slippery slope, though a well exposed hard rubber clarinet is easily spotted.
That said, the stamps on your clarinet speak to a bakelite composition, and I suspect you are right in your assessment.