We just started carrying Freecap Disposable Helmet Liners. They do a lot to keep the liner of your helmet clean, and stay in the helmet pretty good.
In their promotional materials the manufacturer brings up a lot of good points about how they are hygienic, comfortable and useful, and also market it to eliminate this problem:
"Why fight with your partner for a hair of different colors found in the helmet?"

https://scooterpartsco.com/new-products/freecap-helmet-liner-box-of-8