The invention relates to a hair colorant comprised of a flowable, aqueous preparation of oxidation colorant intermediate products and a flowable, aqueous oxidation agent preparation which are mixed in a weight ratio A:B1:2 to 2:1 to produce a gel-forming coloring batch immediately before applying on the hair. The positions of the two sub-zones are changed, as a result of which the magnetization in the examination zone changes. The apparatus can be configured with a highly conductive sample assembly enclosure. Alternatively, the memory card activates the other interface for detecting a second voltage level of the second buffer when the memory card is inserted into a second card reader, and the second buffer is activated to send the second control signal if the detection is positive.