Answer: Food dye
Notes: A study showed that tartrazine, a yellow food dye, temporarily made the skin of living mice transparent. Tartrazine is a synthetic food colorant, lemon yellow in color, and water-soluble. It is used in dairy products, beverages, desserts, and confectionaries. The dye strongly absorbs blue light, creating its orange-to-red color when dissolved in water. Normally, biological tissues scatter light due to proteins, fats, and liquids. A concentrated tartrazine solution reduced light scattering by matching the refractive indices of tissue components. This allowed researchers to see blood vessels, internal organs, and muscle movements in real time.
