private void Coloring() { string[] lines = richTextBox1.Text.Split('\n'); int i = 0; int totalLength = 0; foreach (string line in lines) { int index = line.IndexOf("#"); if (index > -1) { richTextBox1.Select(totalLength + index, line.Length - index); richTextBox1.SelectionColor = System.Drawing.Color.Blue; } totalLength += line.Length + 1; i++; } richTextBox1.Select(totalLength, 0); }