So after a certain amount of sturm und drang over the subject, I did color my hair. And I'm pretty happy with the results. It was expensive, so I may not do it always, and it smelled funny and took a bunch of time, and next time I'm bringing my own magazines; but it was fun. It's basically been returned to my original color - nothing fancy, just what I had in high school (even my haircut is similar to what it was then). And although I didn't do it because I wanted to recapture the past somehow, the effect is that I keep glimpsing the past out of the corner of my eye, reflected in mirrors and car windshields.
The part of the past that it's caused me to remember is that the dark brown color of my hair was an aspect of my looks in which I always took more or less unalloyed pleasure. I grew gray so gradually that it wasn't something I felt I'd lost, exactly; but I find now that the feeling of pleasure, simple and straightforward, is still there. So I'll keep it for a while, at least, and see how things go.