Adding Text with different color styles in RichTextBox

        
        /// <summary>
        /// Writing to a RichTextBox in different colors should be easy enough. The intiuitional way would be:
        /// richTextBox1.Text += someText;
        /// richTextBox1.Select(richTextBox1.Find(someText), someText.Length);
        /// richTextBox1.SelectionColor = Color.Blue;
        /// Which works but gets messed up when other text is added to the RichTextBox.
        /// Adding SelectedText instead of just Text does the trick:
        /// </summary>
        foreach (string ws in WorksheetsRequired)
        {
            if (this.Worksheets.ContainsKey(ws))
            {
                string ok = "Worksheet " + ws + " found." + Environment.NewLine;
                output.SelectionColor = Color.Green;
                output.SelectedText += ok;
            }
 
            else
            {
                string error = "Worksheet " + ws + " could not be found." + Environment.NewLine;
                output.SelectionColor = Color.Red;
                output.SelectedText += error;
            }

            // scroll to bottom of rtb
            output.SelectionStart = this.richTextBox1.Text.Length;
            output.ScrollToCaret();
        }