My text messages used to be blue between a specific friend, now they are green. Neither one of us have changed settings or updated..both on IOS5.
see third paragraph under imessage http://support.apple.com/kb/HT3529
Messaging between iPhones are blue. Messaging to other devices are green.
we both have i phones ios 5.0.1 or higher.
Did you take a look at the link that I provided.
Check this: Settings/Messages/ Make sure iMessage is On.
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