A Misleading Appearance

Euripides, Children of Heracles 130-131 (tr. David Kovacs):

The clothing he wears and the arrangement of his garments are Greek, yet his deeds are those of a barbarian.

καὶ μὴν στολήν γ' Ἕλληνα καὶ ῥυθμὸν πέπλων
ἔχει, τὰ δ' ἔργα βαρβάρου χερὸς τάδε.

Erasmus, Praise of Folly 17:

An ape is always an ape, even if it's dressed in purple.

Simia semper est simia, etiam si purpura vestiatur.

Cf. C.S. Lewis' phrase "trousered ape."