Fucum facere, originally 'to apply a dye,' in the sense of practising an imposture and deceiving by skilful (sic) pretence, is frequent among good authors. Terence in the Eunuchus: 'Came secretly across another's roof, in order to play a trick on a woman,' fucum factum mulieri, where factum is a supine not a participle. Quintus his brother writes to Cicero: 'If you perceive that a man who has made you a promise wishes to play a trick on you, as they say, you must conceal the fact that you have heard this and know all about it.' For fucus is a species of plant, in Greek phykos, used for dying woollen cloth. Thus fucus may be found meaning simply 'dye,' and fucare 'to colour'; Horace in the Odes: 'coloured with crocodile dung.' Especially if we mean to say that the colour is not natural or original, but artificial or falsely applied, as in Horace again: 'Wool purple-dyed / Never regains the hue it once has lost.' So the cosmetic which women apply to their skin to hide blemishes to their beauty, as if they were putting on a mask, is called fucus; Plautus: 'They hide the body's faults with rouge,' fucus. And just as the fucus is colour added by art, so a mask is not a true face but an applied one. Seneca says wittily 'so that he likes the mask better than the face,' that is, he prefers to seem rather than to be. Lucretius too in book 3: 'Now from the inmost heart true voices come; / The mask is snatched away, the real is left.' Cornelius Tacitus in the Dialogue on Orators: 'Thus there was not lacking an excellent teacher, a man of real distinction, to show the true face of eloquence and not its image.' Thus we say people are 'wearing a mask' when their appearance belies what they really are. And things are called 'eye-wash,' offucias, when they are empty appearances, which trick the eyes of the spectator like sleight of hand. In Greek there is a single word for this kind of imposture, phenakizein, and the noun phenakismos; the contriver of the disguise is phenax. The compiler of the Etymologicum graecum - and a dishonest and corrupt writer he was - thinks the term came from peneke, a Greek word for false hair, which is galericulum in Latin.
Julianus, quoted by Ulpian in the Pandects, book 14 title Ad senatusconsultum Macedonicum chapter 9, used color in the sense of fucus: 'But Julianus adds' he says 'that if any color, any line of defence has been thought up to the effect that the son of the family who was proposing to accept the loan should give a surety.' Experts in forensic rhetoric also use the word 'colour' for a line of argument likely to carry conviction which they have invented for the defence. Juvenal: 'Quick quick, Quintilian, please give us some colour.' And when that great expert is in difficulties, the wife caught in the act defends herself with the most impudent of 'colours' ''Twas agreed of old / You should do what you like, and also I / Should please myself.'