Final answer:
Cochineal was the substance used to produce a valuable red dye favored in European fashion, particularly by the French court.
Step-by-step explanation:
The correct answer to the question of which substance was used to make a valuable red dye greatly valued in fashion by the French court and the European textile industry is cochineal. Cochineal is a red dye derived from the cochineal insect, Dactylopius coccus, which is a parasite on cacti in Central and South America. Historically, it was prized for its deep red color, and the dye was an important item in the trade and commerce of the era.
Indigo, another option listed, is known for producing a blue dye from plants like Dyers woad, but isn't associated with red dyes. Madder is yet another plant-based dye that produces a red pigment but was not as significant in this context as cochineal. Tyrian Purple is a famous dye with a purple hue that was indeed used by high society in ancient times especially in Byzantine society, but it is not the correct answer in this case. Therefore, d. Cochineal is the correct answer.