hp 28s yellowed keys.

[vaklaff]

Retrobright is the term you may want to look up. I’d suggest videos from a fellow forumer - channel Hey Birt! I could spend days watching his work, amazing!

However applying retrobrighting on a 28’s keys is only for the very brave, simply because taking the calc apart is hard and putting it together in good cosmetic condition is next to impossible…

I wouldn’t worry too much about the colors. Instead, enjoy the machine while it works.

Just my 2 cents