Green Texts
When you send a text to another iPhone user and your sent text messages turn GREEN what does this mean?
iPhone 12 Pro Max, iOS 14
Question marked as
Top-ranking reply
It means he’s “disconnected” from Apple’s iMessage data network and that your phone is attempting to deliver the mesage via SMS text thru your mobile carrier.
See a bit more info in this article:
https://support.apple.com/en-au/HT207006