The breeze buttons adapt to the used colour scheme. They expect to be drawn over
the "Active Titlebar" colour defined by the user.
In the KCM we're mixing roles from the window deco with classic window palette roles.
This leads to a situation where we can draw white on white (or black on black etc)
The KCM currently attempts to resolve this by blending the current decorated button
with the foreground colour text. Unfortunately if you have a white decoration button,
black text and a grey window this ultimately just ends up being grey-on-grey.
This patch instead renders the buttons over the same background used in the
actual window decoration for maximum contrast.