Cuttlefish fluid is a type of INK produced by cuttlefish, SEPIA, octopi, OCTOPUS, INKY, and squids. It is a dark brownish-black color and is used for a variety of purposes, including writing, drawing, and printing. Cuttlefish fluid is composed of proteins, amino acids, and other organic compounds, and it is known for its ability to change color when exposed to light. It is also used as a natural dye for fabrics and as a food coloring.