What to do when the AirPods Pro silicone tips discolor and turn yellow?

I've only ever cleaned them with water. I always keep them in their case and have never left them in the sun. Nothing has ever been poured on them except water to clean them.

Over time, the tips have turned from white to yellow, and water does not clean them. They are discolored and it's really off putting.

Here's a picture comparing new AirPods Pro tips to tips that have been used for a while.