I bought a few sets of those scales at the ebay link. They are beige colored, not white, and consistent color all the way through. The photo is taken in such a way to make them look yellowed but that's not the case at all.
The seller is a complete asshole. I asked about provenance and he berated me, and random other people, basically saying there's no way I could know I've ever worked with legit westinghouse stock, and though his was genuine, none of the other I've used from trusted sources in the past with expected results, was, etc. etc.
It may be vintage "ivory" micarta of some type, may even be legit westinghouse ivorite of some color, but it's not the stuff you're looking for that's white to cream in the inside and yellows over time.