Which word in this excerpt from act II, scene IV, of Shakespeare's Twelfth Night is a reference to a color-changing gemstone, hinting at Orsino's inconsistent nature? CLOWN: Now, the melancholy god protect thee; and the tailor make thy doublet of changeable taffeta, for thy mind is a very opal. I would have men of such constancy put to sea, that their business might be every thing and their intent every where; for that's it that always makes a good voyage of nothing. Farewell.