Yours is a '41 model. Having looked at images now of examples from all of the Varsity's production years, it looks like the earlier ones, such as the one I have, had its ribbon cover trim painted glossy black to contrast the crinkle paint. The 1940 model year seemed to have a very bright trim, perhaps chrome or nickel plated. The 1941 and 1942 models in contrast had a very dull metal trim, so the question remains, what is the trim finished in? ​Having looked at another one of my Royal models from that era, my first guess would be that it's nickel plated. Your observation that it has a "yellow tint" is a classic sign of nickel plating, especially the kind that was done pre-war. Given what was going on at the time your typewriter was made, I wouldn't be surprised if Royal had to cut a few corners on the plating of decorative parts, and why those parts haven't stood the test of time as well.

So you did manage to clean (polish) the ribbon cover trim after all?