Grey. More grey. So very, very grey. That’s the main visual impression left by Robert Carsen’s new production of Verdi’s Aida. Possibly a few older operagoers still think of Aida as a fabulous spectacle: horses, temples, caparisoned elephants and all the gilded splendour of the Pharaohs. But if you cut your opera-going teeth more recently than 1990 – and unless you’re going to one of the more lavish Ellen Kent efforts – you’ll know by now to expect nothing of the sort.