Vout, Caroline, "The Myth of the Toga: Understanding the History of Roman Dress", Greece & Rome, 43, No. 2 (Oct., 1996), p. 215. Published by Cambridge University Press on behalf of The Classical Association. DOI: https://doi.org/10.1093/gr/43.2.204. (Vout cites Servius, In Aenidem, 1.281 and Nonius, 14.867L for the former wearing of togas by women other than prostitutes and adulteresses).
Ziderman, I.I. (1986). "Purple dye made from shellfish in antiquity". Review of Progress in Coloration. 16: 46–52. doi:10.1111/j.1478-4408.1986.tb03743.x.