a friend of mine Steve Boswell suggested PLA+ eSUN 3D Bone white (Knochenweiss)

https://www.ebay.de/itm/403378153725?var=673410941096

I checked it with a RAL Color Reader  and for not yellowed Computer RAL9006 weißalluminium seems to be the best choice.
First try: https://www.ebay.de/itm/174614665194?var=473820383289
is looking good

For 3D Printing I needed the color of the original cases of the XE and ST Series. So I bought a color checking device RAL RAL Color Reader  and a RAL Farbkarte.
I checked several Atari XL Computer in different state of yellowing.

The best looking NOS Atari on the left side has the following colors.

RAL 1013 Perlweiß is best fitting for good looking Atari XL Computer not yellowed

For more yellowed units

RAL 1014 Elfenbein fitts for yellowed units like the right one.

First try RAL 1013

https://www.3djake.de/extrudr/green-tec-pro-natur