David Cameron and Samantha Cameron disembark (Getty)

There is a tendency, among political leaders, especially of the UK-US variety, to engage in covert sartorial diplomacy during state visits; in effect for the visitor to mirror the dress of the visitee in order to suggest a discreet sort of understanding of the agenda — at least as far as photo ops go.

Such was the case when Gordon Brown first came to see Barack Obama, for example (both did that dark suit,blue tie thing), and such was often the case with Tony Blair and George W. Bush. Yesterday, however, when David Cameron showed up for his current US trip, the changed nature of the relationship seemed to be reflected in his wardrobe. One day in, there’s been zero matchy-matchy.

See, for example, the British deplaning, for which Mr Cameron sported a purple tie — a colour yet to be seen on the president, and one that seemed particularly significant, given that a high percentage of the time Mr Cameron favours blue ties, which is also the primary colour of President Obama’s ties. Thus, for Mr Cameron to choose not to wear blue can be read as a conscious declaration of independence. (After all, the deplaning moment is an enormous and unavoidable photo op. It sends signals; see, for example, Mrs Cameron’s choice to fly her national brand flags via a Burberry trench.)