Using this static method you can not access QMessageBox directly, because its created and destroyed entirely inside function. But you may try to alter stylesheet property of calling object before call to this function. This means calling object should be descedant of QWidget...
something like this:
QString tmpStyleSheet=this->styleSheet();
this->setStyleSheet("style sheet for your QMessageBox");
QMessageBox::information(this, "Done", "Well done!!!");
this->setStyleSheet(tmpStyleSheet);
style of QMessageBox will inherit parent's style...