My understanding is that Remington Parkers used the bone & charcoal method during their years of production, never cyanide. It was only after production ceased that Remington used the cyanide process to REFINISH guns. The Parkers you see out there that are cyanide colored are refinished guns. I do not believe Parker Reproductions ever reported exactly what their process was for case coloring, some have speculated with uncertainty. If you've got some data to refute this, please correct me if I'm wrong.
I stand by what I wrote above, corroborated in TPS Vol. 1 on pages 160 & 199. I have what I believe to be all the errata sheets to TPS, nothing in those refute what the authors of TPS originally wrote, nor has there been any documentation refuting that over the past quarter century since TPS was published. Also, in a direct conversation I personally had with Babe DelGrego, several years ago and before he passed, stated that he never did any type of case coloring in his shop as he farmed it all out.