Обработчик пункта меню Color, форма frmmain:

private void mnuColor_Click(object sender, System.EventArgs e)

{

blank frm = (blank)this.ActiveMdiChild;

frm.MdiParent = this;

colorDialog1.Color = frm.richTextBox1.SelectionColor;

if (colorDialog1.ShowDialog() == DialogResult.OK)

{

frm.richTextBox1.SelectionColor = colorDialog1.Color;

}

frm.Show();

}