void BlueCheckBox_CheckedChanged (object sender, EventArgs e)
{
if (_blueCheckBox.Checked) {
_originalBackColor = _richTextBox.BackColor;
_richTextBox.BackColor = Color.Blue;
} else {
_richTextBox.BackColor = _originalBackColor;
}
_backColorValue.Text = _richTextBox.BackColor.ToString ();
}