Why are some comments 'highlighted' while others aren't?

New-ish Lemmy user here (a couple weeks), I've noticed some comments under posts are 'lighter' than other comments. What causes this?

20 points · 7 comments · view on lemmy.world

7 Comments

Barns@lemmy.world · 5 pts · 3y (4 replies)

So they're supposed to mark the new comments that we're created less the 10 mins ago. I'm not sure why you're seeing the other comment highlighted when it's a few hours old, did you follow a link to that specific comment? If so, that comment will also be highlighted

dabster291@lemmy.zip · 2 pts · 3y (3 replies)

I didn't follow any links.

dabster291@lemmy.zip · 4 pts · 3y (2 replies)

Update: the limit seems to be 4 hours for comments, not 10 minutes.

Barns@lemmy.world · 2 pts · 3y (1 reply)

Thanks for the update, where did you find the 4 hours documented?

dabster291@lemmy.zip · 1 pts · 3y

I didn't, I just noticed that 3 hour-old comments were highlighted, while 4 hour-old comments weren't (but I just saw a highlighted 4 hour-old comment and an unhighlighted 3 hour-old comment, so it might be something else).

boulderly@lemmyadmin.site · 5 pts · 3y (1 reply)

I've wondered the same and thought they might be new since my last visit?

dabster291@lemmy.zip · 1 pts · 3y

I just entered the thread, so in that case all the comments should be highlighted.