Opera buffs enjoy their jargon. We all do it, scattering words like ‘spinto’ and ‘Fach’ like an enthusiastic pizza waiter with an outsize peppermill. It’s principally a means of signalling that you’re part of the club. But occasionally it’s genuinely useful, and Glyndebourne’s new production of Verdi’s Luisa Miller had me thinking about the concept of ‘tinta musicale’, a term used to describe Verdi’s sense that each of his operas should have its own distinctive sonic colour.