C# RichTextBox color text

RichTextBox rtbLog = new RichTextBox();

public void AppendText(string text, Color color)
{
    rtbLog.SelectionStart = rtbLog.TextLength;
    rtbLog.SelectionLength = 0;
    rtbLog.SelectionColor = color;
    rtbLog.AppendText(text);
    rtbLog.SelectionColor = rtbLog.ForeColor;
}
...

AppendText("[" + DateTime.Now.ToShortTimeString() + "]", Color.Red);
AppendText(" ");
AppendText(userid, Color.Green);
AppendText(": ");
AppendText(message, Color.Blue);
AppendText(Environment.NewLine);