Google has tweaked the overall look of the button at the Android program of Gmail.
However, I argue that the bottom-right of this display is a spot for the central button of the app.
I neglect the button there Because I would instead write emails from my notebook, where the web interface of Gmail gets the button on the left.
While I do have to write the new email, my mind expects the button to be with my messages along with the remainder of the controllers of Gmail.
They are relatively popular, so I am ready to admit that I am the one with the issue here. However, those programs utilize contrasting colors to assist the screen pops off, a cube. Google uses buttons and is based heavily on differentiating them.