Look, by the time you can actually see gray hair, the change already happened weeks ago inside the follicle.
Your hair doesn't just randomly lose color. There's an actual process.
Pigment gets made by these specialized cells deep in your scalp, and as new hair grows, that pigment gets passed into each strand.
When that process slows down or stops completely, the hair just... comes out clear. No pigment. That's gray.
At first it's just a few strands here and there. You barely notice.
But put yourself under lighting—especially in photos or video—and suddenly that lack of pigment becomes super obvious because it bounces light differently than everything else.
That's why it stands out way more on camera than it does when you're just looking in the mirror.