Green vs blue texts iPhone4s

Just noticed this. Outgoing texts within a convo are sometimes in a blue bubble and sometimes in a green bubble. One convo they even changed midway through. What's the deal? What does is mean? Phone Post 3.0

Blue is iMessage. Means the other person has an iPhone. Sometimes if it won't go through it'll resend an iMessage as a text. Phone Post 3.0

The blue bubble is an iMessage to an iPhone, iPod, or iPad. The green bubble is a standard text message. An iMessage is the default way that apple products communicate with each other. Phone Post 3.0

Great! Thanks! Phone Post 3.0

Some other things to think about.
iMessage is a service provided by Apple and does not cost you a message. They are essentially Instant Messages and are sent over the Internet.

Text messages are sent over cellular towers and are handled by your cell provider.

The Government has stated that IM services, such as iMessage does not have an expectation of privacy, therefore they can obtain your iMessages from Apple without a warrant.
Text messages, on the other hand, DO have an expectation of privacy, and the Government needs a court order to get them from your cell provider. Phone Post 3.0