I think some strains just do it for no reason. I've seen pictures of a brainwreck plant from highgrade-seeds that had pink hairs. I'm sure it will be fire.
I grew a Powerplant this year and about two weeks into flowering, all the hairs turned pink. Over the next month or so, the color deepened into a dark purple. Now that it's cured, though, theres no trace of the color left over, except one or two hairs here and there that didn't die back to the standard red-orange pistil color.