It is possible to use food coloring to dye protein fiber fabrics, such as wool, silk and nylon. Food coloring is known as an acid dye as its mild acidity helps it bond with the material.
Food coloring, such as the kind sold in the bakery aisle at the grocery store, is useful to dye animal fibers. Crafters may also use powdered drink mixes to dye protein fibers. However, food coloring cannot dye cotton or other synthetic fibers, except for nylon. It is commonly used for tie-dyeing wool yarn after soaking the yarn in a mixture of water and vinegar for half an hour.