Provided is a hair dye that can be discharged from a non-aerosol foamer vessel into a favorable foam, and even if the discharged foam is applied to head hair by being rubbed in by the hands, the hair dye has favorable foam retention by the liquefaction of the foam during hair dyeing processing being suppressed. The hair dye comprises: a first agent containing an alkaline agent and a second agent containing an acidic agent. The hair dye is used by discharging a liquid mixture of each agent of the hair dye in the form of a foam from a non-aerosol fomer vessel. When the foam discharged from the non-aerosol foamer vessel is agitated as-is under specific agitation conditions, the ratio (b/a) of the volume of the foam (b) when 40 minutes has elapsed post-agitation with respect to the volume of the foam (a) immediately after agitation is within the range 0.7-1.
