How to clean discoloured speakers + rubber trim

UV damage results in physical changes in the color and possibly the finish texture. I don’t think that there is a practical way to reverse this process. I think that a final step in the build process applies a topcoat that has been damaged. You’d need to strip and reapply the topcoat, but there could also be damage to the layer under the topcoat.

It’s a contrarian approach, but you could swap the player locations and eventually they will begin to look similar.

I have used this trim restorer on my vehicle to return sun faded plastics to black.  It’s basically a temporary dye, rather than a cleaner.  It doesn’t last but a couple months on a car, but I would think would last much longer on an indoor product.  On a vehicle, it does seem to work better on harder plastics than the soft/rubbery pieces.  The dye is rather thin, so I wouldn’t put on a cheap rag and apply rather than put directly on your speaker.

To be clear, I have not used this on my own speakers and not guaranteeing it will work well. Just offering ideas.