Green text on iPhone 6s

Texts will be green if the recipient does not have an iPhone, or if they have iMessage turned off on their iPhone.

Or if you have iMessage turned off in Settings/Messages, or you are not signed in when you go to Settings/Messages/Send & Receive.

jaunita33 wrote:

my 6s iPhone spontaneously started texting through my iCloud account, showing my texts in green instead of blue. how do I return the phone and texting to its previous state

ref:

Set up iPhone to get SMS messages on Mac

Forward SMS/MMS text messages from your iPhone to ...

Messages for iPhone, iPad, Apple Watch, and Mac

What is the difference between iMessage and SMS/MMS?

What is the difference between iMessage and SMS/MMS? – Apple Support (UK)