>It's also trivial to refute-- if I'm wrong then the messages OP is sending from their custom box should show up with a blue background in iMessage on the recipient's iphone. Is that the case or not?
The distinction that the iOS messaging app uses to set the color of the message bubbles is whether messages are sent over SMS/MMS or iMessage. Since they're sent over iMessage, the message bubbles will be blue.
But yes, adding Matrix to the mix does add more potential failure points, since there are now two messaging protocols involved instead of one. That's just the nature of bridging messaging protocols though.
The distinction that the iOS messaging app uses to set the color of the message bubbles is whether messages are sent over SMS/MMS or iMessage. Since they're sent over iMessage, the message bubbles will be blue.
But yes, adding Matrix to the mix does add more potential failure points, since there are now two messaging protocols involved instead of one. That's just the nature of bridging messaging protocols though.