Earlier quoted context omitted.
Good for you but understandable user interfaces are (and should be) higher priority than prettiness; the "warning button" looks like a warning message for me. But of course there are alternatives for visual clues that still look flat-ish: http://i.imgur.com/jXN2tpe.jpg
It only takes mousing over the button to get an indicator that it can be interacted with. That combined with placement should be sufficient to communicate purpose.
The new Blackberry OS is like this with gestures. Sure, you can spend 20 minutes moving your finger(s) in every way imaginable to learn how to use it because there's no chrome (or hardware buttons), but it certainly doesn't instill confidence on the first use. Instead, it presents itself as a challenge: "learn how to use me, I dare you."