For the Japan state dinner, first lady Michelle Obama wore a floor-length gown in a brilliant shade of purple by designer Tadashi Shoji. The dress was sleeveless and feminine with a delicate V-neckline and a fitted bodice embellished with feathery embroidery. The skirt was full and flowing. It was a party dress — pretty, polite and resolutely traditional.

It was also a beautiful example of fashion diplomacy.

On a night when the White House was celebrating the culture and traditions of Japan, Obama chose a gown by a designer who was born in Japan and came to the United States in the 1970s when he was headed to college. Shoji, 67, built his business in Los Angeles, where he gained a reputation for gowns on the red carpet. But he is very much a part of Seventh Avenue; he presents his collection in New York and is a member of the Council of Fashion Designers of America.

He is an egalitarian designer. His work is not dominated by rarefied pieces that sell for thousands of dollars — though he produces a high-end runway collection that displays his deft touch for detail and keen eye for figure-flattering construction. He offers a bountiful selection of evening gowns that are priced in the hundreds of dollars. He does not solely create clothes for lithe professional models and their real-life doppelgangers. He is also a reliable purveyor of glamour for plus-size actresses and moguls such as Octavia Spencer, Queen Latifah and Oprah Winfrey.

Shoji’s work is not provocative or subversive. It is accessible. Obama’s dress was directly from his fall 2015 collection, which was presented in February. It had been dutifully altered from the more translucent runway iteration to a discretely lined one.

President Barack Obama and first lady Michelle Obama smile at each other as they wait to greet Japanese Prime Minister Shinzo Abe and his wife, Akie Abe. (Jacquelyn Martin/AP)

Shoji was not at the White House when his dress made its appearance at the North Portico. (Obama also wore one of his day dresses earlier in the afternoon.) He was traveling in Shanghai. But he noted, through his publicist, that he was, of course, “honored to have the opportunity to dress Mrs. Obama, especially for such an important engagement.”

The selection of a gown for a state dinner is always a matter of sartorial politics, cultural exchange and U.S. Chamber of Commerce-style marketing. The choice is, at heart, an expression of pride in American creativity and craftsmanship. In the past, Obama has chosen less established designers, such as Doo-Ri Chung. And Obama’s state dinner dress was a nod to the youthful vigor of Seventh Avenue. This time, by selecting a low-key veteran such as Shoji, the dress served as a celebration of the workaday traditions and longevity of this country’s garment industry.

The state dinner dress is also an acknowledgment of the honored country — an appreciation of its aesthetics and talent. So, in the past, Obama has chosen dresses by designers whose “hyphenated lineage” are part of our cultural mosaic: She wore a draped, violet gown by Chung, who is Korean American, to the state dinner honoring former South Korean president Lee Myung-bak.

Obama has highlighted the work of foreign-born designers who have set up shop in New York, underscoring the importance of economic diversity and the fluidity of the global marketplace. The first lady wore a dress created by Indian designer Naeem Khan to the dinner in honor of former Indian prime minister Manmohan Singh, and she wore a dress from New York-based Marchesa — founded by two British designers — when the White House welcomed British Prime Minister David Cameron.

The stature of the gown also explains the profound disappointment expressed by American designers when Obama wore a red printed dress by British designer Sarah Burton of Alexander McQueen when the White House hosted former Chinese president Hu Jintao. The dress acknowledged neither American designers nor the international stature of New York as a fashion capital. It was a psychic blow.

Like the inaugural gown, a state dinner dress is a symbol. The first lady, on this night, stands in for the warmth and humanity of the American people. She gives no formal toast. She is not expected to talk policy or politics. She is the gracious hostess, the charming dinner companion — uncomplicated proof of our goodwill.

Presisident Obama and first lady Michelle Obama welcomed Japanese Prime Minister Shinzo Abe and his wife at the steps of the White House for the state dinner in Abe's honor on Tuesday. (AP)

Her role is, perhaps, neither modern nor politically correct. It is wholly situated in the stereotypes of “the better half” and “the gentler sex.” And perhaps, the days are numbered for a role burdened with such cliches. But even if some day soon there is a gentleman standing in this position, a man whose tuxedo will carry significant cultural freight, there always will be a need — a desire — for the civility that is represented by the formality and pomp of the evening.

Getting dressed up doesn’t change a person’s fundamental nature, but formal dress requires time and intention. There are rules that beg to be followed. It is slow fashion. A woman doesn’t just throw on a gown, and a man rarely keeps his cuff links and studs rolling around atop his bureau. What to wear? What to wear? That is the fretful lament before a formal occasion — the one time when even those who stubbornly think that fashion doesn’t matter suddenly come to the conclusion that their appearance does.

They don’t necessarily want to look cool or hip or sexy. Fashion that is too cutting edge or progressive can come across as haughty and distant. Intellectual fashion can be exhausting. People just want to look appropriate, which is to say that they want to be polite. And so often, that means that fashion at state dinners is rather dull — as it was Tuesday night. Starlets turn down the wattage. Power brokers refrain from swaggering. Entertainers — whether Ciara or Shonda Rhimes — dress for the chorus rather than center stage. There is an overabundance of basic black.

Guests arrive for one singular evening draped in good manners and respectfulness. And at a time when both so regularly go missing, the value of personal diplomacy can’t be ignored.