Word in this excerpt from Act II, scene IV, of Shakespeare's Twelfth Night which is a reference to a color-changing gemstone, hinting at Orsino's inconsistent nature is 'opal'.
Feste when compares Orsino to taffeta, he suggests that Orsino should display what he is in person through his clothing. Feste expresses his view that Orsino is "changeable" and that "thy mind is a very [opal.]" Therefore, he concludes that Orsino is someone that he cannot be relied upon just like an opal, which looks in different colors from different angles. Hence as an opal, Orsino change is perspective with what encounters him. As Orsino has no directions, therefore, Feste suggests his life be well suited on the sea "put to sea" as it will takin his "intent" wherever it would.