Matthew Guay explains that @media (prefers-color-scheme) works in roughly 42% of email clients, including Apple Mail, Outlook, and Fastmail, which covers most opens since Apple Mail alone handles 65% of them. Gmail, Outlook on Windows, Yahoo Mail, and Thunderbird ignore it, and Gmail on mobile inverts colors on its own. Avoid pure black and pure white to keep clients from inverting, and test in real apps.
Ask a nerd: can emails include dark and light mode themes?
