Sir Thomas Browne (Religio Medici, p. 67) rationalises this into “hair-dye.” The reference is to Medea renovating Æson, father of Jason, with the juices of a concoction made of sundry articles. After Æson had imbibed these juices, Ovid says:
Barba comæque, Canitie posita, nigrum rapuere, colorem.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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