rmula (I) and thedioxazine compounds of the formula (II); mixed withB) at least one member selected from the anthraquinone compound group represented by the following formula (III) in the free acid form: ##STR397## wherein Z.sub.4 is --SO.sub.2 CH.dbd.CH.sub.2 or --SO.sub.2 CH.sub.2 CH.sub.2 L.sub.3 in whichL.sub.3 is a group capable of being split by the action of an alkali, wherein the amount in