I agree on removing it, since it turned out not to work well despite lots of people trying.
On your particular question, there's the client hint Sec-CH-Prefers-Color-Scheme: https://web.dev/user-preference-media-features-headers/
On your particular question, there's the client hint Sec-CH-Prefers-Color-Scheme: https://web.dev/user-preference-media-features-headers/
I don't see this header being sent in Chrome 104!
Note that the server has to request that header using accept-ch.
curl --head https://sec-ch-prefers-color-scheme.glitch.me/
HTTP/2 200
date: Fri, 19 Aug 2022 18:55:43 GMT
content-type: text/html; charset=utf-8
content-length: 936
x-powered-by: Express
accept-ch: Sec-CH-Prefers-Color-Scheme
vary: Sec-CH-Prefers-Color-Scheme
critical-ch: Sec-CH-Prefers-Color-Scheme
etag: W/"3a8-iEB3drxZIB7EZYHQL534qwomDuI"