1. IN A PROCESS FOR COLORING FIBROUS MATERIAL CONTAINING NITROGEN AT ROOM TEMPERATURE WITH DYESTUFFS THAT ARE AT LEAST DISPERSIBLE IN WATER IN THE PRESENCE OF AT LEAST ONE SURFACTANT SELECTED FROM THE GROUP CONSISTING OF NONIONIC ETHYLENE OXIDE CONDENSATION PRODUCTS, CATIONIC COMPOUNDS CONTAINING A QUATERNARY NITROGEN ATOM AND NINIONIC AND ANIONIC COACERVATING AGENT, THE IMPROVEMENT WHICH COMPRISES BRINGING THE MATERIAL TO BE COLORED INTO CONTACT WITH AN AQUEOUS PREPARATION CONSISTING SUBSTANTIALLY OF 4 TO 30%, CALCULATED ON THE TOTAL WEIGHT OF THE PREPARATION AND 100% STRENGTH ACID, OF AN ALIPHATIC CARBOXYLIC ACID WITH A MOST 5 CARBON ATOMS THEN STORING THE MATERIAL SO TREATED FOR AT LEAST 10 MINUTES DURING WHICH TIME THE MATERIAL IS PREVENTED FROM DRYING WHEREUP IT IS FINISHED OFF BY BEING WASHED.