Natural Hair & Gray Strands Turning Back to Black

Since I have gone natural, I have had an increasing number of gray strands on the right side of my hair. In the beginning, I thought that it was just some gray strands. But, I found that many of the full strands were inconsistent in color.  My hair would be black from the roots, and gray towards the ends. My co-worker suggested that the sun had bleached some of my hair. This seems like a reasonable explanation; it has happened to me before. But, it could also be genetic. I did some research online and found out that this could be caused by diet and stress. I also remember having changing gray to black hair when I was a freshmen in college. I was stressed out from classes ; it makes perfect sense. This is a reminder to me that hair and body are affected by more than just products that we use.  Did this ever happen to you?