If you want the yellowing to go away so it looks better when you go to sell it, remove the door and paint some hair bleach paste on it(obtainable form beauty supply shops, eg. Sally Beauty), tape some saran-wrap sealing it in so it doesn't dry, and let it sit in the sun on a good day.

This procedure is used by those restoring computers from the 1970s and 1980s where the beige has turned to bisque. Here is a video from The iBook/8-Bit guy. He uses an UV light, you can use a sunny day, other people have achieved similar results as such.

Same thing with my previous white WP fridge, compactor, GE gas dryer, and Sharp microwave.  All turned yeller.  Mother's Roper fridge same thing.  The plastic grid on my kitchen door window too.  The white vinyl tile in my kitchen and bathroom has turned as well.  It has to be from the UV light coming in my windows because wherever I had a bathmat or area rug...didn't turn yeller under it!