https://www.cdc.gov/niosh/npg/npgd0180.html
CDC - NIOSH Pocket Guide to Chemical Hazards - o-Dianisidine
Dianisidine, 3,3'-Dianisidine, 3,3'-Dimethoxybenzidine Colorless crystals that turn a violet color on standing. [Note: Used as a basis for many dyes.]
niosh pocket guidechemical hazardscdcdianisidine