I don't know if there would be a historical anecdote about Robespierre's hair--seeing as he always had it powdered, any color change would probably go unnoticed. Out of curiosity, do we know at what point in his life the lock is supposedly from?

(Note: The hair going naturally white may just be a slight fixation of mine after finding this summer among my dark hair a strand of white that appeared to corespond in legnth to the ammount of time I'd been in college so far...)