Provided is a hair dye that has no problems with foam formation during discharge from a non-aerosol foamer vessel or post-discharge bubbling of foam over head hair, and does not cause skin staining. The hair dye, which has water as a medium, comprises: a first agent that contains an alkaline agent； and a second agent that contains an acidic agent. The hair dye is used with the a mixture of the agents being discharged in the form of a foam from a non-aerosol foamer vessel, and the surface tension of the mixture of the agents before discharge is in the range of 30-50 mN/m under specific measurement conditions.
