hp 28s yellowed keys.

[Rafa]

I recently got an hp hp 28s and noticed straight away that the keyboard is darker than how this model appeared in photos and videos.
the white keys are yellow, the shift button is so dark it is closer to reddish purple than the rich red color i see on other hp 28s, even the plate of the keyboard seem darker und duller.

I'm wondering if this is the effect of the chemical reaction of UV and the fire retardant bromine that was used in plastic in those old days, or a production batch that used a darker hue?
Although yellowing as a chemical reaction is the more likely explanation, i included the second possibility just because, to my eyes, the darker appearance of the calculator is consistent throughout, i.e the plates, grey keys, cream keys, and red shift key are all harmoniously of a darker tint.

It is not a big drama for me but rather a small disappointment as i wanted to have the 28s, in small part, because the overall look and the combination of the rich red, light cream, and grey color scheme of the keys made for a very attractive and visually pleasant aesthetic (to me at least).

Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

Thanks!