We had stains on ours, probably from the DS window being left open during a drizzle.
The wife took them off, soaked them with (I think) Shout stain remover and let them sit for a couple of days. Washed on cold-gentle, dried on gentle and ironed them after that. They look and hang like new.
BTW, it was a bit of a pita re-hanging them...at least for me since I kept skipping a hanger and would have to remove most of them to get to the missed one.
Ken