Before iMessage was released all text messages sent from iPhones were SMS/MMS. They were all green. If an iPhone recipient is unavailable via iMessage a text will fall back to SMS. So green bubbles are intentional, they indicate a text was sent via SMS.

> The puke-green text bubbles from android and calm-blue bubbles from iMessage

This quoted bit is actually incorrect. All messages from android and from iMessage are in identical gray text bubbles.

The blue/green bubbles are for your own sent messages only