First, dyes are colored organic compounds that can dye dimensions or other substrates into a certain color. Most of them can be dissolved in water or organic solvents, and in the dyeing into a soluble state, for the transparent color liquid state, directly or through certain media substances and fibers and fibers to occur in the physical and chemical combination of coloring on the fiber, mainly with the object of the dyeing and printing.

    Classification of dyestuffs: solvent dyestuffs, disperse dyestuffs, direct dyestuffs, basic dyestuffs, cationic dyestuffs, sulfide-reduced dyestuffs, acid dyestuffs, reducing dyestuffs, reactive dyestuffs and so on.

    Second, pigments are organic or inorganic colored compounds insoluble in water and general organic solvents. Powdery substance used for coloring. It does not dissolve in water, grease, resin, organic solvent and other media, but it can be evenly dispersed in these media and can color the media with a certain covering power. Pigment itself has no affinity for fiber, and it can only be colored by adhesive or film-forming substance to make it attached to the surface of the object or mixed inside the object.

    The history of the real dye industry should start from the discovery of the first synthetic dye-"aniline violet" by the British chemist Perkin who was only 18 years old in 1856, and the development has been more than one hundred and fifty years since then. At that time, due to the development of the textile industry, there was an urgent need for dyestuffs, and the natural dyestuffs were far from meeting the needs in quantity and quality. In addition, the discovery of organic aromatic compounds in coal tar provided a variety of raw materials needed for the synthesis of dyestuffs, and at the same time, the theoretical modeling of the fourth-order carbon (1858) and the structure of benzene (1856) was established, which enabled the people to carry out the organic synthesis in a well-planned manner. It was the several opportunities mentioned above that led to the emergence and development of the modern dye industry.

    Light and color: The color of dyes is the complementary color to the color of the light waves they absorb (spectral color), and it is the reflection of their light absorption properties in people's vision. The relationship between the color and structure of dye molecules is essentially the relationship between the light absorption properties of dye molecules and their structure.