WATCHING Donald Trump on TV early last week, I got a shock. He read from a teleprompter. He sounded like a statesman — well, sort of. He kept the boasting to a minimum. He held the taunts in check.

But what really threw me was his hair. Its color was as muted as the rest of him. I saw flecks of pale silver where I’d grown accustomed to showy gold. For a fleetingly presidential moment, he had a fittingly presidential mane.

The evolution of Trump’s coiffure over the decades has been widely noted and thoroughly documented. He has parted his hair on one side and then the other. He has combed it forward, swept it backward, swirled it like frozen yogurt, aerated it like cotton candy. In a brisk wind, it has been a pair of gossamer wings. During a tense debate, it has been a gargantuan sponge.

But less frequently observed is how much its hue changes, and I don’t mean from one year to another. I mean from one day to the next, in more incremental and mesmerizing ways, to a point where no two observers can agree on what to call it.