A student preparing to explain indigo dyeing writes down these points: - Blue indigo pigment is not readily soluble in water. - In a low-oxygen dye vat, indigo is chemically reduced to a pale, soluble form. - That soluble form penetrates textile fibers. - When the wet textile is removed and exposed to air, the dye oxidizes back into insoluble blue indigo. - The blue pigment then remains trapped in the fibers. Which choice most clearly explains why fabric emerges pale but turns blue in air using only information from the notes?