There was a famous psychological study looking at in-groups and out-groups (us vs them mentality). They tested people with completely arbitrary differences. Things like giving some people short pencils and others tall pencils to see what would happen. Before long, those with similar pencils colluded together finding other similarities to bind them as a group. Not only that, but they looked down on their counterparts.

The famous "Robber's Cave" study looked at this as well: https://www.simplypsychology.org/robbers-cave.html

They've found this pattern everywhere and with everyone, child, adult, every ethnicity. It's how we are wired. Team Apple. No fuck you, I'm team Android. Windows vs macOS. Consoles are better than gaming PCs! It goes on and on and on. Blue bubbles vs green bubbles. Even if Apple switched the colors, it wouldn't matter. People would still be pissed text messages got blue.

There's also one huge factor no one talks about: green is not Android. Green is SMS. Since there is no interoperability between Android RCS and iMessage yet, it comes in as a standard SMS.