RCS is a new green? If you’re referring to the existing SMS green, that was Apple’s original color for messaging. They adopted blue to represent the transition to iMessage. So you can’t say they picked a poor color on purpose; it was representing their own product originally before they even came up with iMessage.

End to end encryption is a reasonable justification for a visual indicator.

Is having your message be a different colour really a punishment?

I mean prior to iMessage existing, all messages sent in the "Text" app were green bubbles.