Discoloured tail ligt lens

[Gary70]

My O/S real lens has a slight yellow tinge. It is inside where the bulb goes and not the outer shell.
It isn't terrible but because the other side is lovely and shiny it stands out, especially on the reverse light (to me at least).

I don't have a problem taking the lens out, but wondered about ideas to shift the the yellow and what might be the cause/remedy, rather than take it out and fumble about with glass cleaner for hours.