This meme that it's "just about the color of the bubble" has got to die.
Messaging over SMS is way worse in every way. Group messaging breaks inconsistently in ten different ways, you have issues with attachments, you miss a bunch of other features, etc.
When you text in groups as much as teens do, these things matter. Not being able to use half the features you regularly use because one person in the group chat is Android is going to be legitimately frustrating.
What's interesting, however, is why the US population has settled on iMessage for premium messaging features, instead of WhatsApp like so many other countries.