private void HighlightWord(RichTextBox rtb, string word, Color color) {
            int startIndex = 0;
            while (startIndex < rtb.TextLength) {
                int wordStartIndex = rtb.Find(word, startIndex, RichTextBoxFinds.None);
                if (wordStartIndex != -1) {
                    rtb.SelectionStart  = wordStartIndex;
                    rtb.SelectionLength = word.Length;
                    rtb.SelectionColor  = color;
                }
                else
                    break;

                startIndex += wordStartIndex + word.Length;
            }
        }