Hmm, good question. I have to color my hair also because of gray now. I guess it's because I don't want to look older than I feel.
I just watched a show last night where the woman was obviously letting her gray grow out. She was a prosecutor.
Lets see, 2 things go through my mind when I notice, sometimes simultaneously,
1. I wonder if they're just too busy in their lives to take the time or to care anymore.
2. I think it's purposeful and I admire them for it.
I suppose any further thoughts about it would depend on the whole package, i.e. if their whole head is gray there's a good chance they've decided to go with it either way.
Maybe try letting your gray grow out/in and see if you like the way it looks. You can always dye it again later.