This sort of thread is why I have little interest in Internet forums anymore. Subjects that are easily settled but never stop coming back from the dead.
When it comes to discolored rubber stems, the most fundamental chemistry possible, easily referenced by anyone---known as "oxidation" or "rust" to the general public, and "redox" to the scientific-minded---is endlessly disregarded/ignored in favor of Secret Information of Unknown Origin. It's the PipeWorld's version of the Flat Earth Society.
Ebonite/vulcanite turning green is a chemical process that alters the material at an atomic level and cannot be reversed. (Theoretically in a laboratory, yes, but nothing remotely practical under any conditions, never mind a pipe or pen workshop).
The only way the oxidized ebonite can be functionally returned to its original color is to physically remove the discolored surface layer by scraping, sanding, or chemical means until unoxidized material is reached.
Chemical means is pointless effort since it leaves a pebbled, textured surface that must be scraped or sanded back to level in its own right.
The end.
No magic, no secrets methods, no secret chemicals.
The closest thing to an instant fix is stain or dye. While it can work acceptably on things like old radio cabinets; on pens, telephones, or pipe stems---objects subject to handling wear---all you get is a mess.
As for the rims of pipes looking new again with spit and a rag, while there might be some instances where it will work, in most cases it will not. It depends on what needs removal. If it is built-up hard carbon, discolored finish, or darkened wood, stronger measures are required up to and including reconstruction (topping and refinishing).