Accent palette role doesn't work in style sheets

#include <QApplication>
#include <QFormLayout>
#include <QFrame>
#include <QWidget>

static const QStringList kNames = {
  "alternate-base",
  "accent",
  "base",
  "bright-text",
  "button",
  "button-text",
  "dark",
  "highlight",
  "highlighted-text",
  "light",
  "link",
  "link-visited",
  "mid",
  "midlight",
  "placeholder-text",
  "shadow",
  "text",
  "window",
  "window-text"
};

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);

  QWidget window;
  QFormLayout *layout = new QFormLayout(&window);
  foreach (const QString &name, kNames) {
    QFrame *widget = new QFrame(&window);
    widget->setStyleSheet(
      QString("QFrame {background: palette(%1)}").arg(name));
    widget->setMinimumSize(32, 32);
    layout->addRow(name, widget);
  }

  window.show();
  return app.exec();
}