Here are a few tweets courtesy of email developer Gary Wesolowski.
One major issue I've seen so far affects emails that already have a dark background. These are being converted to a light theme look 🤔
https://twitter.com/gj_wes/status/1185085607569231874

Definitely some colour inversion filter on PNG images. Really visible on the flags in Duolingo email
https://twitter.com/gj_wes/status/1185106494687236096

I still don't have the dark theme option on my account so I can't have a deeper look at this right now.
Here are a few tweets courtesy of email developer Gary Wesolowski.
I still don't have the dark theme option on my account so I can't have a deeper look at this right now.