How about Modern for Hacker News: https://www.modernhn.com/ - available for both Gecko and Chromium-based browsers. There's also a Wikipedia version: https://www.modernwiki.app/ - tho now it just slightly redefines already modernized interface that was released months ago
Another one that was made recently by a user: https://news.ycombinato.com/
That's an interesting nested comments visualization with it getting darker. I would guess it's stacked alpha instead of different colors.