You be warned, try this NOT on your working installation of Qt, you need to reinstall it.

1.) Create a new widget application project

2.) Create a new funktion in mainwindow.h

void setColor(QColor value);

Now refactor on QColor (!!) and Type QFont. This is what i have done accidentally and not

on purpose. But the effect is horrible, because in the QColor is changed to QFont and 

can't be undone.  It is necessary to deinstall Qt and install again, because the installer has no repair option.

Exclude the entire Qt installation folder from refactoring!