static void OnLineNumbersForegroundChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TextEditor editor = (TextEditor)d;
var lineNumberMargin = editor.TextArea.LeftMargins.FirstOrDefault(margin => margin is LineNumberMargin) as LineNumberMargin;;
if (lineNumberMargin != null) {
lineNumberMargin.SetValue(Control.ForegroundProperty, e.NewValue);
}
}