Or you could use meaningful button labels:
<format> <cancel>
(or something like that)
It's both intuitive and simple. Universally every HIG[1] that exists advocates that. Personally, I'd make the button red as well.
[1] Human Interface Guidelines.
For example, here's relevant section in KDE's HIG: http://techbase.kde.org/Projects/Usability/HIG/Messages#Conf...
EDIT: To clarify I didn't suspected this to be a revelation to anyone. I just wanted to put it here, since it's a very relevant audience and I was just surprised nobody have mentioned it already.