It looks like in iMessage for business, the phone’s user’s outbound messages show as dark grey (as opposed to normal iMessage and SMS/RCS which show outbound messages as blue and green respectively). I assume this is supposed to communicate that you’re talking to a different sort of entity, not a normal person on a phone.

Personally I don’t see why you’d care. My business isn’t trying to pretend to be a normal person using a phone, so why would it matter?

https://www.apple.com/ios/business-chat/

I’ve never seen a gray bubble and have received incoming messages from all different types of accounts

Incorrect.