The presidential State of the Union address has always been a moment of political theater on a grand scale, full of soaring rhetoric and pageantry as well as policy and partisanship. Only recently has it also become a costume drama, with supporting players using visual cues to make their voices, and positions, heard — even though they aren’t officially supposed to be speaking at all.

Only recently, that is to say, have the clothes in the room played such an obvious part in the politics of the room. It is dress that goes far beyond the traditionally patriotic red-white-and-blue ties and suits that have been the default uniform of legislators past.

It began during the last administration, in 2018, when Democratic congresswomen donned black in solidarity with the #MeToo movement. Many members of the Congressional Black Caucus also wore kente cloth draped around their necks in protest of President Donald J. Trump’s statements regarding Africa and Haiti, and red pins in honor of the death of Recy Taylor, a Black woman raped as a child by a gang of white men who were never brought to justice.

It continued the following year, with the coordinated effort of female representatives to wear white in honor of the suffragists, recognition that they were the largest class of women to enter Congress, and a riposte to the West Wing. Happened again, in 2020, during the SOTU that took place during Mr. Trump’s first impeachment trial, with many women members of Congress again wearing white.

So it probably should not have been a surprise that during President Biden’s first official address, many legislators donned blue and yellow to telegraph their solidarity with the citizens and government of Ukraine as that country fights back against the Russian invasion.

If one example of something is a fluke, two a coincidence and three a trend, four may qualify as a tradition.

Indeed, even before the S.O.T.U. address began, many congressmen and women were tweeting their wardrobes. Not as a frivolous distraction, but as a point; and not just for social media, but for posterity.

The State of the Union, after all, is one of the moments on the political calendar made for public consumption, preserved as part of the official record. Details matter.

Representative Victoria Spartz of Indiana, who is Ukrainian American, wore a bright blue jacket over a butter-yellow dress. Elaine Luria, of Virginia, wore a pale yellow jacket over her blue dress. Her fellow Virginian, Abigail Spanberger, paired her blue dress with a bright yellow necklace. Lori Trahan, of Massachusetts, wore a blue suit and yellow scarf, posing with fellow congresswomen before the address.

Nancy Pelosi, the speaker of the House, sitting at President Biden’s left shoulder, was in a bright blue pantsuit; on her lapel, a pin with the American and Ukrainian flags intertwined had replaced her usual Mace of the House pin.

Chuck Schumer, the Senate majority leader, wore a yellow tie with his navy suit. So did Representative Mark Takano of California, who added a light blue shirt. Assorted members wore ribbon pins, passed out by Representative Mike Quigley of Illinois, co-chair of the Congressional Ukrainian Caucus. Some carried little Ukrainian flags.

And the first lady, Jill Biden, in the balcony with Oksana Markarova, the Ukrainian ambassador to the United States, among her guests, wore a bright blue satin bias-cut dress (made in New York by the designer Sally LaPointe) with a yellow sunflower, the national flower of Ukraine, embroidered on the sleeve. Ms. Markarova wore navy blue.

In the dark, woody chamber of the Capitol, the colors stood out, unmistakable. Especially in contrast with the Republican red dress of Representative Marjorie Taylor Greene, visible when she rose to yell an objection in the middle of Mr. Biden’s speech, a fashion choice as calculated as her action.

(Vice President Kamala Harris’s chocolate brown Sergio Hudson was harder to parse.)

At a time when so much information is received visually, sent in snapshots over social media networks as frozen moments in time, such choices resonate: immediately recognizable, before any words are read or uttered.

Clothes, of course, have long been used as tools to symbolize unity and affinity by groups of all kinds, from the military to protest organizations. Worn together as a uniform, they send a message that is undeniable.

They are one of the few universal modes of communication we have, one that is available to almost all, and that can be read by any viewer — now, and in the future. As a medium, visuals are shared, in every meaning of that word. In a world that is both more connected and more splintered than ever, that is a very powerful lever. One that there’s no question elected officials will continue to push on, again and again.