Acid dyes refer to dye molecules containing acidic groups, also known as anionic dyes, which can combine with amino groups in protein fiber molecules through ionic bonds and are suitable under acidic, weakly acidic or neutral conditions. Mainly azo and anthraquinone structures, a few are aromatic methane structures. Dyes and colors are generally compounds that have their own color and can make other substances obtain bright and firm colors in a molecular or dispersed state.