[chrismorgan]

This is basically what email clients have been settling on doing, recently—though they have the luxury of working with a static resource, and not needing to handle any dynamic stuff.

https://litmus.com/blog/the-ultimate-guide-to-dark-mode-for-... is a good article about this. We just released this sort of functionality for Fastmail’s webmail within the last few days, too, matching what Litmus calls a partial colour invert. We find that it doesn’t satisfy quite everyone, but the overall experience is much improved. I myself use light mode for my work email and dark for my personal email (partly to distinguish them, partly so I’m testing it—otherwise I’d prefer light mode), and this general approach has produced very good results in all but one case I’ve experienced so far (and that one was still acceptable).