Can you share your light one? I've never been able to find a white background scheme I actually love, rather than tolerate...

I prefer my background dark so light colorschemes are not really an area I've explored seriously. Also, dark colorschemes are much easier to design than light ones due to the disproportionate amount of light a white, say, background emits compared to the amount emitted by text. It dramatically reduces the number of colors you can use.

I have one here: https://github.com/romainl/vim-sweet16 but it is intentionally weird and essentially unmaintained.

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We have many millenia of books using black text on a white background with various colors added, why are computer monitors all of a sudden so special and annoying

Because paper is naturally pale. So it would have been silly for people to colour them black.

And because monitors are giant light bulbs. So a large white background is harder on the eyes than black.