The point I want to make is that Messages is not preventing them from including Android users because they don't have an iPhone, which is a general misunderstanding that I often observe when talking with Android users who use Whatsapp or similar and is also recurring here. If the Android user gets locked out, it's because a human decided to, not because Messages refused to include that user based on ecosystem lock-in (unlike Whatsapp).
However, like Twitter OP, I can testify that teens attach a lot more weight to the blue/green than they should. But then again, it's everywhere in popular culture. Try finding a recent hit movie/TV series or music video, produced in the US, that shows green bubbles (or Android for that matter, even though it has a higher market share).