There is a kit my son bought at Lowe’s, that he changed the color from yellow to white. Homax tub and sink refinishing. Worked very well.
Looking at the caulk, buttons, and hose, I would guess they were all white.
Here’s a good article, explaining why it happens. Scroll down to “Using Hydrogen Peroxide…” to read about a rather convoluted bleaching process, using peroxide and UV light.
https://mobilehomeliving.org/yellow-bathtubs-in-mobile-homes/
But I’m guessing, replacement is the easiest solution.
Source: Question: Was my shower always that color or is it that color from age?
