If you transplant gray hairs from the body, will they be the same color on the scalp?
Hairs grafted from one location to another do not change their color. Generally, the amount of pigment remains the same, as well. This means that if your hair is brown, the grafted hairs will produce brown hair. If the grafted hairs are white, they will grow white hairs upon transplantation and regrowth. With age, hairs loose their ability to make pigment. Some hairs loose that ability before other hairs. For instance, hairs on the side of the scalp loose this ability to produce pigment sooner than the hairs on the top of the scalp or the back of the scalp. Some regions of body hair produce white hair sooner than other regions due to the loss of pigment formation capacity.
The cells that produce pigment are called melanocytes. When the ability to produce pigment ceases, the hairs will turn white rather than grey. Therefore, the term grey is really is inaccurate. Actually, true grey hairs are extremely uncommon, but they do occur due to a decrease in the amount of pigment rather than an absence of pigment production.
Hair also tend to maintain the same diameter as the pre-transplanted area. On some occasions the diameter will be slightly greater upon transplantation and other times the diameter will be the same.