One option is to have a professional remove the dye, otherwise the roots will always show unti all of the dyed hairs have either shed or the dye fades. There is no way to "freeze" the growing process.

I dye my gray/white beard and it is a weekly task to keep the roots dyed as the white is in contrast to my dark brown beard.

My Beard Journey:  http://jefffsbeardboard.yuku.com/topic/25137/Finally-I-have-a-Beard
Beard and Bald Thread:  http://jefffsbeardboard.yuku.com/topic/27831/Beard-bald-head-shaved-head-or-buzzcut
Patchy Beard Success Stories:  http://jefffsbeardboard.yuku.com/topic/33742/Patchy-Beard-success-stories-Before-and-After-photos#.ViujbH7nuM8
Taming the Wild Mustache:  http://jefffsbeardboard.yuku.com/topic/30822/Taming-the-Wild-Stache#.Vj_Mh7erTIU
  
Last Edited By: Slybeard Jan 3 14 1:33 PM. Edited 1 times.