Problem with richTextBox colour

Question

Hi, im trying to make a very simple syntax highlighter, just highlight some keywords, but i cant get it to work, this is the code i hav so far

private void richTextBox1_TextChanged(object sender, EventArgs e)
        {
            Regex r = new Regex("\\n");
            String [] lines = r.Split(richTextBox1.Text);
            foreach (string l in lines)
            {
                ParseLine(l);
            }
        }
        
        void ParseLine(string line)
        {
            Regex r = new Regex("[\\s\\t\\n{}():;]");
            String[] tokens = r.Split(line);
            foreach (string token in tokens)
            {
                richTextBox1.SelectionColor = Color.Black;

                String[] keywords = { "program", "begin", "end" };

                for (int i = 0; i < keywords.Length; i++)
                {
                    if (keywords[i] == token)
                    {
                        //richTextBox1.SelectionStart = richTextBox1.Text.Length - keywords[i].Length;
                        //richTextBox1.SelectionLength = keywords[i].Length;
                        richTextBox1.SelectionColor = Color.Blue;
                    }
                }
            }
        }
It seems i have to select the text to colour it, but when i do it then starts from the beggining of the keyword...