It is yellowed and looks grundgee.
I love wet & forget shower. It's a no scrub product that will clean over time.
You could also scrub with either baking soda, barkeeper's friend, or comet.
I used regular cleanser on mine like Comet.
All you can do is clean. Sometimes the yellowing is just from age, plastic does that when it's old.
I would suggest trying an auto headlight cleaner . I got a cleaner from Autozone and my plastic headlight covers were yellowed and grungy and my car is 16 years old. One a month I just clean them to keep them clear .