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What papers say that low contrast is better than high contrast black on white?Not about low contrast being better -- only about (slightly) reduced contrast than full on white on black blaze.
Black on white is better for readability, but the brightness can induce fatigue for longer term use (and people use computers all day long) and also hurt knowledge retention (according to educational related research).
A slightly off-white is better there than shining a white backlight on your eyes for hours on end (and adjusting monitor brightness achieves the same effect, color-wise as having a "less white" background in the first place, and is recommended by doctors).