The consent form that i signed at Asmed before going through the surgery mentioned this point. The hair could grow later on after the tranplant with a color that could be different than the original hair. Also some of the top HT surgeons such as Juan Couto is showing some videos and patient results with some changes in the hair color after surgery.
I've never seen such a large case done exclusively with body hair, much less one that looks this good. Your hair honestly looks much better than some guys I know who still have a decent chunk of scalp hair. I'd be interested to know if you see the characteristics changing at all over time, as I've seen it suggested that transplanted body hair will partially take on traits of the recipient area after a while.