Washed feather pillow and it's gone brown

[Foxmansions]

I just washed a white duck feather pillow at 30C and tumble dried it. It's now covered in light brown stains, evenly distributed on both sides. Is this oil from the feathers? And how can I get it white again? It's not very old, was pretty clean except for one small coffee stain, and from John Lewis.

Think about it this way: does it matter once you have put a pillow protector and a pillowcase on it?