Privacy
This site doesn't track you in any way. I don't even like cookies. Seriously though, adverts are designed to rob people of agency and surveilling people for the sake of selling them stuff is warped and pathetic (often there are other, more sinister motives too).
If you changed the colour scheme using a button or the console, the site may
have saved a key in your local storage.
You can remove this using your browser's "clear site data" functionality or
by opening the console and typing localStorage.clear() (then hit
Enter).