Great question! I did a google search and found a WebMD that gave answers, (or non answers) to that question:
When chemo ends, experts say, it’s very common for the hair to grow back differently.
“We don’t know how chemo affects the cell cycle,” says Dr. Doris Day, an attending dermatologist at Lenox Hill Hospital in Manhattan and author of Forget the Facelift (Avery Penguin 2008). “But the thing is that chemo does seem to affect the hair cycle. After chemo, the hair may start cycling differently.”
Radical color changes—brown hair turning red, for instance—don’t seem to happen, doctors say. But straight hair may go curly, or curly hair straight. White hair may go dark again, or dark hair go white. Hair may grow back thicker. In rare cases, it may not grow back at all. Sometimes, the hair reverts to its original color and texture after a year or two. Sometimes, it doesn’t.
And often, as a recent New York Times article chronicled, patients choose to change their hair color after chemo.
But except for those artificial salon dyes, the whys and wherefores of these hair changes remain unexplained. Maybe it’s just one more way that cancer is like Forrest Gump’s box of chocolates: You never know what you’re going to get. Or why.
See full article: http://blogs.webmd.com/cancer/2012/03/your-hair-after-chemo.html