I think that pure white (255) and pure black (0) should be using extremely sparingly. #FFFFFF? Why not #f6f6ef or #eceff4? Lower contrast can improve legibility, too much contrast can hinder it. #000000? Why not #121821, a dark shade of blue? Nothing in real life is perfectly dark.
Thankfully HN has remained pleasingly off-white.
> improve legibility
Hilarious how this downvoted comment proves it is not. (Update: it became black again)
There should be a special place in hell for those light-grey-text-loving designers.