我有一个改前景的菜单，单击后改变TextArea里文字的颜色，但错误，不知为什么？
菜单事件如下：
void foregroundMenuItem_actionPerformed(ActionEvent e) {
Color color = JColorChooser.showDialog(this,"Foreground",TextArea.getBackground());
if(color != null){
TextArea.setBackground(color);
}
this.repaint();
}
错误如下：
java.lang.IllegalArgumentException: Invalid mnemonic index: 3
at javax.swing.JTabbedPane$Page.setDisplayedMnemonicIndex(JTabbedPane.java:1805)
at javax.swing.JTabbedPane.setDisplayedMnemonicIndexAt(JTabbedPane.java:1385)
at javax.swing.plaf.basic.BasicColorChooserUI$PropertyHandler.propertyChange(BasicColorChooserUI.java:234)
at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(SwingPropertyChangeSupport.java:264)
at javax.swing.event.SwingPropertyChangeSupport.firePropertyChange(SwingPropertyChangeSupport.java:232)
at javax.swing.JComponent.firePropertyChange(JComponent.java:3814)
at javax.swing.JColorChooser.setChooserPanels(JColorChooser.java:446)
at javax.swing.plaf.basic.BasicColorChooserUI.installUI(BasicColorChooserUI.java:79)
at javax.swing.JComponent.setUI(JComponent.java:449)
at javax.swing.JColorChooser.setUI(JColorChooser.java:209)
at javax.swing.JColorChooser.updateUI(JColorChooser.java:220)
at javax.swing.JColorChooser.(JColorChooser.java:183)
at javax.swing.JColorChooser.(JColorChooser.java:171)
at javax.swing.JColorChooser.(JColorChooser.java:162)
at book.book.(book.java:48)
at book.Application1.(Application1.java:12)
at book.Application1.main(Application1.java:45)
Exception in thread "main"
