The rage of feeling hard done by, is how I read this. I like ‘disguise fair nature with…’, meaning you have to overcome your happy nature to drum up some fake fury. That final ‘etc’ gives it away as a feint.
‘But when the blast of war blew in their ears, they imitated the action of the tiger, stiffened the sinews, summoned up the blood, and disguised fair nature with hard-favoured rage, etc.’
Source: Patrick Leigh Fermor, A Time of Gifts (London: Penguin Books, 1977), p. 129