For eyebrow transplants - what if the hair from the back of your head is grey, will the eyebrows have to be constantly dyed?

Transplanted hair retains its original characteristics. So if your donor hair is curlier, thinner, or a different color, it will be the same once it is transplanted to the new area. If your head is totally gray and there are no colored hairs left, you will either have to dye your eyebrows, live with gray in your brows, or find an alternative treatment plan.

The transpanted hair will have the same characteristics as the hair on the donor area. Therefore it will gray as the donor hair does. The good news is the hair in back of scalp is generally late to turn gray. In addition, if/when it does turn gray, they hair can be dyed or colored.

The donor area hair will contain the same genetics when it is transplanted in another region.  There is a phenomenon referred to as recipient area dominance where the transplanted follicles will adapt to their newly transplanted regions by growing longer or shorter, but their color will stay the same.  So if you obtain grafts that are grey, they will grow grey follicles and you would need to dye them to your liking.