I just had a similiar experience with bleaching stains on expensive linens. Was foolishly thinking of linen purchases from a more personal standpoint like "I'll buy really good sheets so they last for years". Ha! Second guests to use them and they are ruined, time to think more like a host. It looks like puppets had a party, how else does one explain bright orange and yellow stains on light purple sheets!? This thread was very helpful though, had no idea acne cream could do this and I assume it is the culprit. The guests say the stains were there upon arrival, but I never would have made up the bed with sheets/pillowcases like this. Also I don't use bleach or any of the products reported to cause this sort of staining.
I filed a resolution report with airbnb, but I'm already feeling like pursuing this is more trouble than it's worth. The guests are denying involvement which is impossible as they were the only ones in the space. I am a new host and a bad review at this point will be a real blow to my listing. I'm already regretting not eating the cost. It's hard not to react when money is flowing out of your pocket, but in the future I think i will let these sort of things go especially for longer reservations. The lesson I learned here is to buy good but inexpensive sheets that are white and pick my battles more carefully. Sigh