iMessages being weird

I have a 13 pro max and currently up to date with iOS 15.5. Now my iMessages seem to have changed from blue to green with all the people that I have messaged who have iPhones too. I’m very confused as to why this happened. Why the change all of a sudden? By the way I’m perfectly connected to my WiFi, no hassle about that if anyone asks. It’s still showing a green send button.