Historically, SMS messages have had green bubbles since the iPhone was introduced in 2007. When Apple introduced iMessage in 2011, the showed iMessages in blue,

Historically, SMS messages have had green bubbles since the iPhone was introduced in 2007. When Apple introduced iMessage in 2011, the showed iMessages in blue, and maintained the green for SMS messages. They are not “cross-platform” messages, Messages only does SMS and iMessage. If you did some reading, instead of getting upset over the longstanding colour of a chat message, you’d know this and not be so angry. Or, like th rest of the world, you would already be using an alternative.