Reducing color removal agents: commonly used ones are insurance powder and Rongalite. They achieve the purpose of fading and decolorization by destroying the color development system in the dye molecular structure. For example, the azo group of azo-structured dyes can be reduced to amino groups and cannot color. However, the damage of reducing agents to the color development system of certain structural dyes is reversible, such as the color development system of anthraquinone structure, so its fading is recoverable.