I guess that it’s the iPhone’s messenger app? I heard that in that app, fellow iOS users have blue bubble messages and Android / other users have green bubble messages, and all the teens in the US /maybe Canada think it’s lame if you don’t have blue bubbles.

Oh. I remember hearing about that about 15y ago, didn't realise it was still a thing. I suppose because I haven't heard of anyone using iMessage for almost as long!