[nequo]

The “natural” background for text is light though. Hard to find books, newspapers, or magazines that put a dark background behind text of any significant length.

Accordingly, the Xerox Alto had a light background too, back in the 1970s. Demonstrated here with Smalltalk:

https://youtu.be/NqKyHEJe9_w

And here with a GUI based text editor:

https://youtu.be/2Z43y94Dfzk

[kps]

As did Engelbart's NLS, as seen in ‘the mother of all demos’. https://www.youtube.com/watch?v=yJDv-zdhzMY

What little actual research exists suggests dark on light is more readable for people with normal vision. People with cataracts benefit from light on dark, and people with astigmatism benefit from dark on light.

[citrin_ru]

Light background for books IMHO is no more natural than dark background for old CRT displays - both are what works best for a given medium: while making dark paper is not harder than light one, it is hard to make a pencil or ink which would be clearly visible on black paper (white markers do exists but they are a recent invention). Blackboard and chalk where natural until we got plastic whiteboards and easy to erase markers.

Modern screens are more or less unique in not limiting background colors so we can use any and and argue which one is better.

[citrin_ru]

Actually there is at least one more common media where we can freely choose between dark and light (at least in the last 100+ years) - guide signs on roads. Both options are common (e. g. white on green/blue and black on white). But even if there are studies showing which background is better for signs it is not necessary the same for a computer screen: road sign should be legible from a maximum distance under variety of conditions - from a sunny day to LED lighting at nigh or heavy rain. Legibility is the main design goal. Computers on other hand are usually used in an environment where we can control lighting to some degree and a distance is fixed. Legibility is important but comfort is important as well (choose of colors should minimize eye strain / fatigue in case if it can affect this).