I do notice a pattern of misunderstanding that I've also observed when talking with Android users IRL. iMessage is very different from Whatsapp. For starters, there is no dedicated iMessage app. iMessage is managed from the iOS Messages app, which handles both iMessage and SMS. It's very good at managing both from one unified interface. In fact, it's so good that it uses arbitrary coloring of messages so you can see…
Why do you think the kids don't like it when a thread is green? Do you think that the kids just don't like the color green? That's not it. They don't like it because the thread being green is an indicator that nearly everything about the group chat experience is going to be worse. Messages will be drastically slower, they will have a higher failure rate, pics/videos sent over that chat will be lower quality, there will be no typing indicators or read receipts, there is no ability to label the chat, likes and other message indicators are more cluttering, etc.
It isn't just high school kids, either. I've seen people at work intentionally exclude android users on group chats because we needed fast responses from people and the 2-3 second delay each way on MMS (and that's best case. sometimes it can take minutes for a single message to go through, if it goes through at all) is intolerable when you're trying to have a fast paced conversation with many people. I've had my friend group (people in their 20s, 30s, and 40s) intentionally exclude android users because they were tired of always worrying if one of their MMSes wasn't actually received by everyone in the group (in groups with android users, MMS failures happened enough to have multiple ruined plans because some people in the group never got all the messages being sent).
This is not just a human problem. These people aren't excluding Android users just because they think blue is a cool color and they want to bully green people. They're doing it because there is a very clear technical issue with SMS where it is very lacking in features compared to iMessage. The colors just happen to be a very easy way to signal whether or not you will be using the superior iMessage or the inferior SMS/MMS.