Xu Collection, Middle Volume Radical: Green (qīng) Dian Kangxi strokes: 16 Page 1382, Entry 02 According to the Sound Rhymes (Jiyun), pronounced dian (falling tone). To dye using indigo plants. According to the Compendium of Materia Medica (Bencao Gangmu), the scum that floats on the surface of indigo plant juice is called indigo flower.