I understand that the blue border around image thumbnails means a post has yet to be approved and green means it has been, but in the help/FAQs I cannot find but am curious about, are for instance when you have some blue, some green, and yellow.

Wondered about this for years since I have been on e621 and now actually posting my stuff on e6AI im more interested.

Apologies for asking a should be obvious question.

Green and yellow are for parent and child posts, respectively. Or perhaps vice versa. I don't remember.