You can be on stock but you're going to need root. Layers are compatible on marshmallow. Search layers manager on the play store.
Without root, you're stuck with the eye blinding white.
Why does Google not want us folks to have OS wide Dark theme? I do not understand at all. Please someone tell me. Why should anyone have to root their phone just to have a dark theme. I thought Android was all about options?
My eyes bleed even on KitKat when i open Gmail or messaging app at night.
What's wrong with Google. Also i want to rant about how the YouTube app sucks but that's for another topic.
STOP READING.
Come on whenever I see root I stop reading what is after that. I though iOS was bad but things you can do on iOS you need to root on Android like backup.
Anyway I doubt Android will ever support a dark theme which is stupid. Only hope more apps support dark themes which I all switched too.