I don't think it could go entirely unnoticed if it had - even if he was incredibly diligent about powdering his hair, I assume it would have been visible, if only, say, at his execution. I don't know anything about the lock - but I've just found this (http://books.google.com/books?id=jeAmWNkmpHUC&printsec=frontcover) (pg 78) on google books:
A lock of Robespierre's hair has just come into the hands of the keepers of the Musée Carnavalet in Paris, and will in future be exhibited in that place by the side of the portrait of the Terrorist painted in 1783 by Boilly. Robespierre in that picture . . . is represented as a young man with finely-chiselled features, blue eyes, carnation lips, and light chestnut hair . . . The lock of hair is of the same colour as that in Boilly's picture. It was enclosed in a locket or medallion, on which were engraved the word " égalité," the date of the "9th Thermidor," and the martyr's palms. The souvenir belonged to Robespierre's sister Charlotte, who, on the death of the Terrorist, was sheltered by one of his adherents, the Citizen Mathon. Charlotte Robespierre, in May, 1834, died in a garret in the Rue de la Fontaine, and left the relic to Mathon's daughter, from whom it passed into the possession of a '48 man named Gabiot, whose son has handed it over to the Carnavalet M.
So! That gives us a bit more information. Er - I'm not sure about the 'light chestnut hair' in the portrait (if it's the one that comes up when I search - incidentally, there is no portrait of Robespierre by Boilly in my big fat catalogue of the Musée Carnavalet, but I have a feeling I'm being way too dorky and should get back to the point), but either way, if in the 19th century the hair was supposedly that colour too, perhaps it supports the idea that it lost its colour over time? Also - I don't know if the "9th Thermidor" is there because the hair was clipped at the time of the execution, or just because it went with the theme of martyrdom, but perhaps it helps.
no subject
A lock of Robespierre's hair has just come into the hands of the keepers of the Musée Carnavalet in Paris, and will in future be exhibited in that place by the side of the portrait of the Terrorist painted in 1783 by Boilly. Robespierre in that picture . . . is represented as a young man with finely-chiselled features, blue eyes, carnation lips, and light chestnut hair . . . The lock of hair is of the same colour as that in Boilly's picture. It was enclosed in a locket or medallion, on which were engraved the word " égalité," the date of the "9th Thermidor," and the martyr's palms. The souvenir belonged to Robespierre's sister Charlotte, who, on the death of the Terrorist, was sheltered by one of his adherents, the Citizen Mathon. Charlotte Robespierre, in May, 1834, died in a garret in the Rue de la Fontaine, and left the relic to Mathon's daughter, from whom it passed into the possession of a '48 man named Gabiot, whose son has handed it over to the Carnavalet M.
So! That gives us a bit more information. Er - I'm not sure about the 'light chestnut hair' in the portrait (if it's the one that comes up when I search - incidentally, there is no portrait of Robespierre by Boilly in my big fat catalogue of the Musée Carnavalet, but I have a feeling I'm being way too dorky and should get back to the point), but either way, if in the 19th century the hair was supposedly that colour too, perhaps it supports the idea that it lost its colour over time? Also - I don't know if the "9th Thermidor" is there because the hair was clipped at the time of the execution, or just because it went with the theme of martyrdom, but perhaps it helps.