Messaging

One or more of the following may apply-

• The person you sent the message to doesn't have an Apple device.
• iMessage is turned off on your device or on your recipient’s device. To check if iMessage is turned on for your device, go to Settings > Messages > iMessage.
• iMessage is temporarily unavailable on your device or on your recipient’s device (weak signal, perhaps).

If you can't send or receive messages on your iPhone, iPad or iPod touch – Apple Support

hello_321 wrote:

I sent a message to someone, but it didnt go through so i sent it as a Text Message, but now whenever i text the person it is still green but messages through others is blue. How can i get it back to blue messages?

You get it back whenever said person turn imessage on their phone or they are connected to a strong wifi/cellular connection. The issue is not on your end, so nothing for you to do.