"Apple could fix that
by implementing RCS, " Uh, no. Implementing RCS would not change the Blue/Green bubble bru-ha-ha. Blue vs green is there to identify the service being used by the messaging app, iMessage, to make the user aware of the capabilities available. Blue, iMessage, secure. Green, SMS, plain text. The GSMA standard RCS is no more secure than SMS, though it has more wiz-bang features. Googles proprietary adapted version of RCS is point to point encrypted, but relies on Google servers. Google's Messages is just like iMessage, in that it uses Google's proprietary adaptation of RCS between capable platforms and reverts to SMS for those that don't support Google RCS.