Abstract: A process for the preparation of a water soluble food-grade diaminotriphenylmethane colorant containing from 2 to 4 sulfo groups, comprising anodically oxidizing the corresponding leuco compound in an electrolysis cell divided into an anode space and a cathode space in the presence of from 0.01 to 2% by weight, based on the solution being oxidized, of a C.sub.2 -C.sub.4 -alkanol, urea, a urea derivative or a mixture thereof, at a potential .epsilon..sub.h .ltoreq.1250 mV and at a temperature .ltoreq.+40.degree. C. The colorants obtained are produced in high yield and are of food quality.