Blue=iMessage, Apple's messaging service
My IMessages on my iPhone6, to one particular person used to go through as blue and said 'delivered'. Now, for the last couple days when I send a text, they sit there as blue, and maybe 3-5 min later, they automatically turn green and get 'Sent as Text Message'. Green is for an SMS Text Message The green background or Send button indicates the message will be sent as a regular SMS text using the messaging plan provided by your cell phone provider. Regular texting rates will apply, based on your texting plan. The SMS text message is automatically used when sending a text to someone without an Apple device.
Green=SMS/MMS, your carrier's messaging service
Green messages (SMS) between iPhones usually indicate that there isn't an Internet connection, hence iMessages aren't working; it might also be the case that the person you're talking to no longer has or has never had iMessages enabled. Since you mention the messages turning from blue to green it means that you used to text via iMessages.
Grey is just the color of incoming texts.
When you send to someone else who is also using iMessage, as long as there is a good network connection (Wi-Fi or cellular), it should send as a blue message. That means it's passing through Apple's messaging server instead of your carrier's. You can also send/receive messages with iPads and iPods if they use iMessage.
However, if for some reason iMessage is not available, the phone will try to send as a regular SMS/MMS message, which will be green. This will also happen if you send a text to a non-Apple device, like an Android or Windows phone.
When Your Text Message Is Green
Nov 3, 2013 2:58 AM