HN has some really non-obvious UX, between this and the mysterious green usernames I still don't understand. And the fact that only some users can downvote. Or the weird logic behind which words cannot appear in titles.
A comment has a green username if at the time of commenting the author was new. The colour remains. If you look at your first comments, you will see them green as well.
YCombinator founders have their own colours which are only visible to each other.
There are plenty of undocumented features like this one.
Both are mechanisms to dull the potency of new users until they have a chance to learn how HN is expected to work.
This might sound gatekeeping, and it literally is, but consider than HN signup is open and takes 15 seconds with no verification. HN likes the way HN works and these provide simple rate-limits on destructive or oblivious change.
