Huachi company in response to the needs of users, after six years of continuous research and development, select foreign special raw materials, user-assisted machine verification, launched the coating after drying in water discoloration paint. The coating becomes yellow after drying and turns blue after contact with water. Optionally reversible or irreversible color. Reversible blue color turns yellow after drying; Irreversible blue color still appears blue after drying. Suitable for plastic, metal, paper, non-woven fabric and other substrates, can use gravure, flexo printing, roll coating, brush coating, spraying and other construction methods. The coating can be self-drying or drying.