It will be interesting to see what color they choose for RCS. Right now, blue indicates an end-to-end encrypted message and green indicates not encrypted. Even when messaging between two Apple devices you can get a green bubble if, for some reason, the message is routed over SMS.
If it were up to me, encrypted RCS would be blue and not-encrypted RCS would be green.
Why do you think that blue represents E2EE and not simply iMessage? If data isn't available and the iPhone sends an SMS, like you mentioned, the bubble is green, but this doesn't necessarily have anything to do with encryption. For example, the satellite SOS messages are represented as gray. It seems more like the color represents the transport.
> iMessages are texts, photos, or videos that you send to another iPhone, iPad, iPod touch, or Mac over Wi-Fi or cellular-data networks. These messages are always encrypted and appear in blue text bubbles.
MMS is email-style MIME messages retrieved over HTTP on a data connection. Push notifications for MMS are delivered as a special SMS, but otherwise it's far far closer to internet than cellular, and it's green.
Gray is encrypted to Apple, and then the information is (of course) shared with third parties. Would you consider that to be a private communication? Kind of. It's a gray area...
I can’t imagine all of the carriers cooperating on key management. That’s probably why some carriers have opted to use Google’s solution instead of their own. I would guess encryption isn’t an option if your carrier isn’t in this group.
AFAICT Google Messages is simply encrypting the data sent over RCS, i.e. RCS is dumb pipes for the encrypted data, and the carries don't explicitly cooperate one way or another. The consequence would be that only users of Google Messages are able to send and receive encrypted messages to/from Google Messages, not other RCS compatible messaging apps. Pretty ironic given the context.
If a customer of carrier A wants to send a message to a customer of carrier B and the carriers aren't cooperating with key management, then I think the message is not encrypted because customer A needs to know B's public key and when B gets the message, they need A's public key to verify the sender.
That's my understanding as well. My original reply was in response to your suggestion that iMessage differentiate RCS encrypted vs RCS unencrypted using colors, and it appears that wouldn't even be possible because Google is applying proprietary encryption on top of RCS using their app.
I find this absolutely hilarious and almost beautiful: Google has been harassing Apple to implement RCS because it's an open standard and because its users feel green bubbles on iMessage are exclusionary. Now Google has implemented a proprietary protocol on top of RCS that only works with its messaging app, and only messages sent between users of that app appear in a darker blue color with a special lock icon.
So Apple will ship the RCS standard in iMessage, and communication between Android users and iMessage will be sent using RCS, but iMessage users will appear to Android users in the lesser light blue bubbles alongside the dark blue bubbles only given to Android users with Google's proprietary app! Huzzah!
If it were up to me, encrypted RCS would be blue and not-encrypted RCS would be green.