Food dyes, such as those in unsweetened Kool-Aid, can be used as acid dyes, for protein fibers, such as wool, or for nylon.
Heat is required.
They do not yield satisfactory results when used on cellulose fibers such as cotton, because they lack the chlorine atoms of the Procion dyes that can react with cellulose, such as is found in cotton, for example. It is important to always follow reasonable safety precautions. The majority of artificial food colorings that have been used over the years have turned out to be at least somewhat harmful when eaten, and have subsequently been banned for use in food.