Blue text message bubbles mean the recipient is using an iPhone and Messages. Green bubbles indicate a non-iPhone OR there was a network issue. I have seen text messages go green to and from an iPhone when there was a momentary wi-fi/cellular issue for the sender or recipient.
Why no beep? Can't say.
On a Mac since 1984.
Currently: 27" iMacs, Macbook Air, macOS 10.14.x,; iPhones, iPods and iPads galore!