XML : richTextbox color of xml File

I have a sting that is actually an xml.

I am using a procedure that gives me the string in a formated way but i also want to have it colorized within the richtextbox. The procedure i am using now is

    private void beautify()  {      //   richTextBox1.HideSelection = false;        richTextBox1.BackColor = Color.White;      richTextBox1.SelectAll();        richTextBox1.SelectionColor = Color.IndianRed;        int firstLine = richTextBox1.Text.IndexOf('\n', 1);        HighlightText(richTextBox1, "<", Color.Blue,true);      HighlightText(richTextBox1, ">", Color.Blue,true);      HighlightText(richTextBox1, "=", Color.Blue,true);      HighlightText(richTextBox1, "\"", Color.Blue,true);      HighlightText(richTextBox1, "</", Color.Blue,true);      HighlightText(richTextBox1, "=>", Color.Blue, true);        string[] str = richTextBox1.Text.Split('\u0022');      for (int i = 0; i < str.Length; i++)      {          if(i%2 != 0)          HighlightText(richTextBox1, str[i], Color.Black,false);      }          richTextBox1.Select(0, firstLine);      richTextBox1.SelectionColor = Color.Blue;    }    

It mostly works with some bugs, but my bigest problem is that for very large xml it is taking way to long. I was wondering if there is a library or something to handle this faster.

Thank you for reading