There are two standard matching systems, Pantone an RAL. The latest is being used more by paint and filament as it does not require paying royalties.Therefore, RAL will be easier to find.
Paint:
Platinum Gray (Apple IIgs, IIc+, Macintosh II, IIvx, Macintosh Color Classic, Classic II, IIci, IIcx, LC)
LVP Powder paint RAL 7044
Filament
Exact match for Platinum gray:
ColorFabb RAL 7044
Very close to platinum Gray:
Polymaker Muted White
Exact match for Apple IIc “Snow White”
ColorFabb RAL 1013
Very close to Snow white:
Warm Lithophane White AF PLA
This is a work in progress.