It’s not literally about the color. The way iMessage works is if everyone in a group chat is using it you can send high quality video and images over it. However if you have a single non-imessage user (i.e. android user) it disabled that for everyone and defaults to MMS video/pic quality. You can see how that would obviously lead to immense peer pressure to not be the one making all of your friends experience worse, or risk just never being in those group chats.