… and now I don’t see the yellow backgrounds anymore, either. Not in litely theme nor in darkly. But now I’m glad of my earlier screenshot, as proof of what a portion of the page looked like, even if you can’t make out any of the content.

When you followed the link to that other post, was that the first time you’d opened it? I wonder if the background shading has anything to do with new comments since the last time a post was opened by you, the reader.

Here’s another post with a lot of engagement: https://lemmy.ca/post/1404816. Right now was my first time opening it.

As of this writing, it has 61 comments. They all, whether top-level or reply-to-top-level, or deeper, have white backgrounds. I’ve saved it to follow, and when/if I see its comment count has risen, I’ll check if any of them have a differently coloured background.

Edit to update, a few minutes later:

Welp, scratch the “new comments since last viewed” hypothesis. I just opened another new (to me) thread: https://lemmy.ca/post/1410603, 134 comments. All over the place: yellow top-level comments, white top-level comments, yellow replies, white replies. Chaos? So it appeared.

Then I tried changing the ordering from Hot to something else, like New or Old. Once rearranged, I noticed that all of the yellow comments – except one – were timestamped as “4 hours ago”. Anything marked as “5 hours ago” or greater had white background.

So, new hypothesis: maybe the colour is an indication of a comment’s age, relative to the time at which you are reading it, with a threshold somewhere between the 4-5 hour mark. That seems an arbitrary figure, but just based on what I observe in that new-to-me post, that’s what I’ve come up with.