There are few moments of political theater as grand as a state dinner, essentially a pantomime of diplomacy and national pride from the set to the staging to the scripts — and the costumes. In that drama, the first lady is cast as both hostess and symbol, her dress a part of the decorative storytelling of the night.

Through the five state dinners of the Biden administration, Jill Biden has seemed comfortable with the hosting part of her (nonofficial) job, but she has never seemed all that excited about the fashion part. In those moments of high public attention and posing, she has most often chosen to wear gowns from traditional White House designers (Oscar de la Renta, Ralph Lauren) that, while elegant, didn’t seem exactly sewn with subtext.

On Thursday, at the state dinner for Kenya, that finally changed.

In a sapphire blue dress covered in sequins, crystals and bugle beads, with a swath of satin across the bodice and sleeves, Dr. Biden played her part. At the official photo op, as she and the Kenyan first lady, Rachael Ruto, flanked their husbands, President Biden and President William Ruto, in matching tuxedos and bow ties, it was the women who stood out.

Dr. Biden’s dress was by Sergio Hudson, a Black American designer who has been a part of the Biden story since the 2020 election. It is the first time she has worn a gown by a Black designer at a state dinner.

Mr. Hudson first became widely known during Mr. Biden’s inauguration, when Michelle Obama wore his plum-colored trousers, turtleneck and greatcoat to the president’s swearing-in. Vice President Kamala Harris also wore a Sergio Hudson look to the inaugural balls — a black sequin column and long tuxedo coat — one of a series of looks by Black American designers she chose to mark becoming the first Black woman to be elected vice president.