What a great question. Two years ago, a dear friend of mine visiting from Europe gave a talk in Washington D.C. Because her husband is a top Physicist in Italy and they both worked at the CERN , she was invited to the Italian embassy to have dinner with the ambassador and his wife. She asked me ( the day before ) if I would like to go, that they had invited me ! I went into a mini panic and had no time for shopping. But I packed a lovely merino wool dress with tuxedo ruffles down the front, nice jewelry and a colorful scarf. I also wore a merino wool blazer with inverted seaming and a peplum. I wore a trench ( it rained ). I felt perfectly comfortable. ( I should say that the Ambassador was called away for something urgent. His wife stayed and was dressed lovely in charcoal grey wool pants, lovely shoes, a black cashmere sweater and a lovely vest with a little metallic in it. She looked beautiful. She had great hair and skin. My friend also wore black pants and a bright color jacket with a scarf and looked beautiful...I was the only one in a dress. : )
I feel that if I have a nice black dress with seaming to give it shape and an interesting detail, a scarf, jewelry ( I have plenty of both ) and black pumps, I can go anywhere.