What is what does it mean when imessages turn green?

When iMessages appear in green instead of blue, it indicates that the message is being sent as an SMS/MMS message instead of an iMessage. This typically happens for a few reasons:

• The recipient is not using an Apple device: iMessage is an Apple-exclusive service, so messages sent to Android phones or other non-Apple devices will always be sent as SMS/MMS.

• iMessage is disabled on your device or the recipient's device: If iMessage is turned off in the Settings app (under Messages), all messages will be sent as SMS/MMS.

• The recipient's device is not connected to the internet: iMessage requires a data connection (Wi-Fi or cellular data) to function. If the recipient's device is offline, the message will be sent as SMS/MMS if that option is enabled in your settings ("Send as SMS when iMessage is unavailable").

• There is an issue with Apple's iMessage servers: Although rare, temporary problems with Apple's servers can sometimes cause iMessages to be sent as SMS/MMS.

• The recipient's phone number is not registered with iMessage: If a recipient has recently switched from an iPhone to a non-Apple device, their phone number might still be registered with iMessage. This can cause messages to be sent as iMessages initially, but if they aren't delivered, they may fall back to SMS/MMS.