I'm inclined to disagree. They're using the color sparingly to call attention to the most important parts of the interface. Coloring compose with the standard gray for the other buttons would mean it is lost in the interface and difficult to see. I like it quite a bit.

I totally agree. My thought was "does my ass look big in that compose button?"

I don't mind the modern hot-orange. It's a great colour for feature highlights etc. But as a button background it just screams "ERROR".