How dyes bind to fabric

I read this information from Organic Chemistry. To be classified as a dye, a compound must be colored and it must bind to fabric. There are many ways for this binding to occur. Compounds that bind to fabric by some type of attractive forces are called direct dyes. These attractive forces may involve electrostatic interactions. The type of interaction depends on the structure of the dye and the fiber. Thus, a compound that is good dyeing wool or silk, both polyamides, may be poor for dyeing cotton, a carbohydrate. Wool and silk contain charged functional groups, such as NH₃⁺ and COO¯. Because of this, they bind to ionic dyes by electrostatic interactions. For example, positively charged NH₃⁺ groups bonded to the protein backbone are electrostatically attracted to anionic groups in a dye like methyl orange. Cotton, on the other hand, binds dyes by hydrogen bonding interactions with its many OH group. Thus, Congo red is bound to the cellulose backbone by hydrogen bonds.