I was a medium brown and always dyed it when I started to get the grey. I remember I did the same thing to see what my roots looked like at age 60, I think. I was so tired of the dying and I was beginning to get thin spots and that is from years of dying.
I decided to keep what hair I had left even if it was grey, better than bald.
My six inch roots looked horrible but I perservered and let it grow out. I shampooed every second day and put conditioner and some shine product and just kept it high up in a bun.
When it finally gew out to cutting lenght, I was shocked at the color. I love it. My avatar is a recent pic. So be patient and let it grow all the way out and see what you have, there are all sorts of things you can do to make it the way you like.
The style I have now is one that I like very much but it takes some upkeep, so yesterday I had it cut shorter and it is easier to keep up.