iMessage vs text message

[mickeydise]

Hello,
I am wondering why the text messages I have sent to another iPhone 4S user are showing as text messages rather than iMessages? The first 2 messages in the string are in blue bubbles but all subsequent messages are in green bubbles. I'm confused! Any help would be greatly appreciated

Thank you.

 

[bab2010]

Because your iMessage is turned off, or your contacts iMessage is turned off.