If the basic job of a work of art is to be interesting, as I think it is, then Jonathan Yeo’s new portrait of the King accomplished that admirably. No sooner had an image of this big canvas been released to the public than it sparked a million memes. What did it mean, people wondered, that His Majesty’s face emerged from a great abstract field of rose and crimson? Was it a nod to the blood-soaked legacy of empire? A secret signal of some sort of satanic conspiracy theory? A portentous meditation on the blood royal? An anxious reflection on...