There are a million things by kenzo! 
Hi, TinaDunn, Thank you for asking about this. Yes, you should notify your host. And, in future, you should let your host know that you recently dyed your hair. I keep dark brown pillow cases around for that eventuality, but, of course, I can only know one is needed if I’m told. In response to some hosts saying $40 is nothing to spend on replaced sheets, let me tell you, that would eat most of my profit margin for a short stay. For homeowners who consider their Airbnb income “cream on top,” losses like these may seem insignificant. But for renters, like me, who use Airbnb to afford their rents, replacing sheets, pillowcases, towels, glasses, adds up to a huge dent in our Airbnb income. So, yes, please help cultivate an ethic among Airbnb guests of taking steps to avoid this kind of damage and paying for it when it occurs. You felt bad and wanted to do the right thing, Tina. Some folks seem to absolutely not care. What I would do: tell the host right away (so she has time to replace it before the next guest) and leave a $10 bill to pay for the new pillowcase. Remember, she also has to go out on a shopping expedition, so the least a guest can do is pay for the replacement. Thanks.