This blue coloured bubble thing I've never heard anyone outside of Silicon Valley engineers/media mention, but I've heard it extrapolated as a deciding factor to the rest of the world by those same people many times.
I don't think most people actually give a shit about the bubble colour.
For me it's the fact that you can generally see the other person typing in an iMessage, while you can't in normal SMS.
That tells me whether the person is replying right now, so it's worth keeping my phone out, or busy and therefore won't be getting back to me for a while.
No. iMessage has the low entry barrier of SMS, but has features like a real chat app. SMS is not an iMessage replacement. Instead you have to get everyone you message with to change to something like WhatsApp.
I don't think most people actually give a shit about the bubble colour.