https://upload.wikimedia.org/wikipedia/commons/3/37/Colorspa...
The not-triangular shape labeled "2200 matte paper" are all colors representable by reflective materials.
Colors outside of that range can only ever be produced by emissive materials, such as fire, stars, or your monitor.
All the colors your website uses should be from the range of reflective colors, as those are the ones seen in nature, and the ones your eyes are adapted to see.
The same applies also to black/white contrasts. Even vantablack next to a white sheet of paper (which would already be massively higher than any contrast in nature) still has a much lower contrast ratio than your monitor has.
Neither zebras nor white pages in a hardback book emit light, they only reflect it.
What books are you reading that have pure white pages with pure black text on them? At best they are eggshell or an off-white page. Also... books are nature now?
What about black text on white pages in an actual hardback book? But since you referred to nature, what about zebras?