Not quietly, but perhaps just not loudly to everyone around you... an email to the author is a billion times better than another worthless HN comment about color contrast.
wrt marginal design choices like colour schemes I absolutely agree, HN people spend too much time bickering about them. But people who wilfully display static content in such a way that people can't see it should be publicly shamed, pour encourager les autres. It's been a solved problem since 1993.