In Apple's Messages app starting with iOS 7, a green bubble surrounding the text means the incoming message came from a non-Apple phone that uses the standard SMS/MMS text messaging system (see SMS).

After years of forcing all users to message in the same old green speech bubbles, WhatsApp is now opening up its interface to ...

UPDATE: Nov. 17, 2023, 8:22 a.m. EST This article now reflections 9to5Mac's confirmation that Apple is still keeping green bubbles green. Wait, so Apple is actually supporting RCS for iOS?