I am assuming you mean in the script window after opening a .txt file? What happens if you click in the window or do a “select ALL” in the window – is there something there? If so, select all and go to edit menu and change font. Changing color “might work”. If not, select all, then do a command-x. Go to the original text file and copy the text, then past back into the script window to see if that helps.
Michael