They’re supposed to reduce eye strain, but personally I’ve never experienced eye strain from any colour scheme, and suspect it has more to do with the eyesight of the user than the colours involved.
Blacking out the screen in those conditions reduces that strain. But you still have to maintain a good brightness and contrast between the elements otherwise you trade one issue for another.
There's no one size fits all unfortunately. Which is why it's great when developers allow for customization.
That's a really good point.
If I have to use a computer or phone under poor lighting, I turn down the display brightness to match.
Otherwise, I prefer to be in a space where I can read something written on paper. And then I adjust the brightness to match that - not cranked up too bright like I see sometimes.