It will allow servers to know what color scheme the user's system prefers.
https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Sec-CH-Prefers-Color-Scheme
This will help the user by allowing websites to display content in the color scheme preferred by the user if the website is a Markdown blog renderer or something that compiles the HTML server-side without much CSS. This is already supported by Chrome.
