I've seen in a friend how a few gray hairs suddenly started to grow with color again; colored from the root to the middle (no idea what triggered it) and grey from the middle to the tip, due they grow as such on the past. So I'm sure that gray hair (transparent hair?) can be reversed.
I suspect that the researchers in the article may have observed something like this happening and decided to investigate it.
I've seen in a friend how a few gray hairs suddenly started to grow with color again; colored from the root to the middle (no idea what triggered it) and grey from the middle to the tip, due they grow as such on the past. So I'm sure that gray hair (transparent hair?) can be reversed.
I suspect that the researchers in the article may have observed something like this happening and decided to investigate it.