Hello Hairy,
As far as I know, Mauser did not produced magazine with Ivory bottom.
So far I have seen only plastic and wood bottom mounted in the Mauser Parabellum magazine.
Due to the fact that it was possible to customize the Parabellum when Mauser produced them, it is possible that somebody asked for an Ivory magazine bottom.
So far there is no evidence.
Albert, assuming that the grips are around 20 years old, in 50 years I will be 98 years old. Maybe be I will be still around. If yes, I will invite you to check the Ivory color change.
Thanks
Ciao
Mauro