Mother's Back to Black, several coats, let them soak in until the color becomes uniform again then protect all your plastic and rubber with 303 Aerospace. I even use the 303 on my seat. It does not get slick like ArmorAll. gives a nice supple feel that maintains its grip.
They turned white because they where coated with a product like being suggested above. It is best to put nothing on them. Order new doors and never use a product to protect them or to make them shinny. The only think I use on anything black on my Wing is soap and water.