Floating Action Button: make the overlay dark, and rotate the button on press.

I don't know how compliant the dark overlay is with Google's future design, but it really helps the contrast for the white-ish screen that comes in. I don't really like it when static design gets changed by transition design, so I feel something's amiss here. Maybe if the incoming screen had a shadow? Maybe you just can't live-track an unmask like this?