Bava Kamma 101 - Thief Steals the Wool, Dyes It, and Returns It (Torts)

If one robbed wool and liquid dye belonging to someone and dyed that wool with the dye and now returns the dyed wool to the owner – is the improvement of dye considered material?

That is, when the thief returns the dyed wool to the owner, is he returning both the dye and the wool? Or, perhaps, that improvement is not considered material, and thus, he is returning only the wool but not the dye – which has, in effect, disappeared?

The question is relevant when the dyed wool became cheap. Does the thief have to pay for the dye? Talmud doesn't resolve the question.

Art: Outside An Indian Dye House by Edwin Lord Weeks