King Charles III talked eloquently of its historic importance in his speech to a joint session of Congress. President Trump praised it in his toast at the state dinner for the king’s visit to Washington. But nowhere was the special relationship between the United States and Britain more obvious than in the wardrobes of Queen Camilla and Melania Trump. They didn’t just compliment each other. They looked complementary.

Their husbands may have dressed to represent their offices, the king in his trademark Savile Row pinstripes, pocket handkerchief nattily puffed, the president in his red, white and blue. But the women, in their multiple outfits, did a lot of the subliminal work, practically shouting through their seams “hands across the ocean.” For a story that would be told mostly in photo ops and brand values — Trump brand, royal brand, fashion brands — that mattered.

In this at least the queen and the first lady seemed visibly on the same page. And while that may have been expected from Camilla, whose job is built on and defined by symbolism, it was more of a surprise from Mrs. Trump, who often seems as interested in pursuing her own agenda and protecting her privacy (all those hats and coats) as she is in supporting her husband’s or catering to the public eye.

Which may reflect not only the first couple’s well-known esteem for the royals, but also how much the royals understand and can leverage their appeal to the Trumps.

The sartorial outreach started as soon as the king and queen deplaned on Monday, Camilla in a light pink Dior coatdress — Dior being one of Mrs. Trump’s go-to designers and the brand she wore on the first day of her state visit to Britain. Dior, as it happens, is also synonymous with well-appointed luxury. Owned by the French billionaire Bernard Arnault, the chairman of LVMH and a guest at the Trump inauguration, the label is designed by Jonathan Anderson, who is from Northern Ireland. In other words, it ticks both the diplomatic protocol box and the Trump taste box.

And if that wasn’t bonding enough, a Cartier pin on the coatdress Camilla wore had been given to Queen Elizabeth II in 1957 on her first official visit to the United States and features a conjoined Union Jack and Stars and Stripes, a reminder of just how long this particular allyship has existed.

It set the tone for the trip.

The women also mirrored each other’s choices in shade (springlike) and sourcing (local designers) at their first meeting on Monday. The first lady wore a buttery yellow form-fitting skirt suit by Adam Lippes, the New York designer who made her inauguration coat, and the queen, a white Anna Valentine coatdress edged in floral embroidery.

Which turned out to be simply a prelude to the official military greeting the next day, when Mrs. Trump wore white (Ralph Lauren) and Camilla’s mint green look by Fiona Clare, a London couturier, was so pale it seemed white. And the similarities didn’t stop there. The outfits had similar nipped-in besuited lines and were topped with wide-brimmed straw hats that almost matched.

Even more strikingly, Camilla wore another historic piece of jewelry: the Cullinan V brooch, which features an 18.8-carat heart-shaped diamond, one of nine stones cut from the 3,000-carat Cullinan diamond originally given to Edward VII. (Two other Cullinan diamonds were incorporated into the British royal scepter and the imperial crown of Britain.) It was a souvenir from the notional vaults of Buckingham Palace, the place Mr. Trump posted he “always wanted to live,” and a canny nod to the president’s admiration for royal trimmings — and the equation of size with importance.

Still, perhaps no images were as striking in their subtext as those unveiled Tuesday night at the first white-tie state dinner since 2007.

That was when the first lady opted for a light pink strapless gown, also by Dior, just like Camilla’s pink arrival coat. (Coincidence? Doubtful.) And it wasn’t any old pink; it was delphinium pink, delphinium being one of the king’s favorite flowers. (Notably, the dress was custom-made, like Mrs. Trump’s Ralph Lauren suit before it. Clearly, designers no longer have any reservations not only about seeing their clothes bought by the Trumps, but also about working with the Trumps.)

Camilla was also in pink, albeit more of a fuchsia shade, again by Fiona Clare, this time paired with an enormous amethyst and diamond necklace that once belonged to Queen Victoria. The king may have given the president a golden bell as a dinner gift and offered a toast that was a master class in tact, but the queen in her opulent gems gave him something else: the opportunity to feel like royalty for a night.

Fashion, it turns out, can be as effective a tool when it comes to flattery as any words.