Restoring colour to accordion shell

[wirralaccordion]

Is there anything you can use to restore the colour to the cellulose coated shell of an old accordion that has been subjected to sunlight through a window and which has caused the colour to fade?

 

[JIM D.]

The ultraviolet radiation in sunlight will in time cause cellulose to change colors. White cellulose will turn yellow and colors such
as red, green & blue to bleach out. Once this damage is done it's permanent as it permeates the cellulose completely.
The answer of course is to keep the accordion covered when stored out of the case.