What the green bubble tells you
The color is a quick signal about which messaging system is carrying a conversation. Blue bubbles mean Apple’s iMessage service is handling the exchange; green bubbles mean it is not. That can happen when someone uses an Android phone, but also when an Apple user has iMessage turned off or unavailable.
This distinction matters because iMessage and ordinary text messaging do not work the same way. iMessage sends messages over the internet and supports Apple-specific features such as typing indicators and read receipts. Green-bubble messages use a different route: traditionally SMS for text and MMS for pictures or group messages. On newer iPhones, green conversations can also use RCS, a newer messaging standard that supports more features than SMS when both phones and carriers support it.
A color that marks a boundary
Apple could have made every conversation look the same. Instead, it kept the colors separate, making the underlying service visible at a glance. The bubble does not identify a person’s phone as Android with certainty; it identifies a conversation that is not using iMessage.
That boundary also explains why features can change when a green-bubble participant joins a group chat. The conversation may have to rely on capabilities shared by the devices and messaging systems involved, rather than on iMessage’s full set of tools. The green bubble is therefore both a design choice and a small status indicator: it tells you that the chat has crossed out of Apple’s messaging system, even when the messages still arrive in the same app.
