I don't know about color, but I do know that when I had long hair, when I changed my diet, it grew longer. When I became a vegetarian, it grew longer; when I started eating fish again, it grew longer.

Mine has also darkened over the years, from light brown with a lot of blonde highlights, to medium brown with fewer highlights (and a bit of white ). +1 that I've heard that darkening with age is pretty common.