What's the difference between blue and green when texting with an Apple phone?

Iphone (or Apple's ipad, itouch, iphone) can send imessage as long as it is above iOS5 (but the sender must also have iMessage and be activated, and have a network). When sending iMessage, it will be displayed in blue, and when sending operator information, it will be displayed in green (that is, it will be charged) for your convenience. Secondly, the chromatograms of light blue and light green are close, so it is not easy to produce visual fatigue. Looking at light blue and light green for a long time will not affect the visual nerve. It can be said that apple is very human.