You've said in your edit. They use a different colour.

They do this because it's important for the user to know.

SMS isn't encrypted. It also costs a lot to send images via SMS/MMS. The user needs to know, they are using a different chat mechanism.

This is literally the reason Apple changes the bubble color. iMessage is encrypted by default and uses normal data instead of MMS. That’s the indicator.

This entire spiel about bubble color envy is ridiculous. Features are the separation. The media will whip things up with their sample size of a handful of cherry picked anecdotes. But almost every teen has an iPhone and uses iMessage in the USA. Apple has over 80% of that market.

What Google wants is for Apple to implement Google’s proprietary RCS implementation, not RCS proper. Because RCS proper lacks a lot of features that people take for granted with iMessage. That is presumably one reason Google forked it and requires it to run through their proprietary middleware.

Edit: Don’t get me wrong. I would love for an open standard to overtake the proprietary bits from both Apple and Google. But Google is disingenuous here. They are complaining because, despite their efforts, they can’t crack the market. Teens aren’t bitting for Android. iMessage has network effect going on, so Google is trying to crack that open since they can’t get a compelling overall product and ecosystem for a valuable demographic.

I’d rather there be open standards. But that means Google RCS has to change as well.