PURPOSE: To use a color former free from an unpleasant smell and a malodor and having highly ecological safety such as crystal voilet lactone hard to dissolve in vegetable oil by using vegetable oil containing a small amt. of a specific aromatic carboixylic ester compd. as a solvent.

CONSTITUTION: As a solvent dissolving a color former being crystal violet lactone, vegetable oil having a fatty acid residue compsn. with oleic acid residue content of 10-60wt.% is used. 5-40 pts.wt. of an aromatic carboxylic ester compd. represented by formula I (R11 and R12 are alkyl, cycloalkyl, aryl, alkoxy, aralkyl or -CH2COOR) or formula II (R21, R22 and R23 are a hydrogen atom, a hydroxy group or alkyl and R24 is alkyl, aryl, aralkyl, alkylaryl, or alkoxyaryl) is added to 100 pts.wt. of vegetable oil. By this constitution, a desired hue with high developed color density can be obtained.