An iMessage would turn green when it is sent as an SMS message to a non-iPhone or Apple device, such as an Android phone. The green color indicates that the message has been delivered via the cellular network instead of the internet. It does not mean that the text message has not gone through or won't be received. When an iPhone user sends a message to another iPhone user, it typically appears as a blue iMessage. However, if the recipient does not have an iPhone or is not using iMessage, the message will be sent as a green SMS message instead. This can happen when the recipient's phone is turned off, has poor internet connection, or if they have specifically turned off iMessage on their iPhone.