Many people do not understand that the green color stands for SMS and not for Android. And it is important to know th difference because it might cost money if you sent them. Especially when it becomes an MMS because you did send emojis or pictures.
I'm from germany and have flat for basically everything, not for MMS though. And our mobile Internet is EXPENSIVE so this will cost extra money for allmost everyone here. So I need to know this. And a simple color difference seems to be the best option.